Tips for identifying intervals in notation?

I have no problem naming or identifying intervals but I have to admit that, when looking at a piece of sheet music, I am certainly not very quick at it. The reason is that I learned music, as a guitarist, from ear and tablature. I never had reason to learn to recognize intervals and such in scores until I wanted to start writing more than just rock music or hip hop. Now it seems like I could benefit a lot from being able to look at a piece of sheet music and recognize intervals as easily as I could if I were picking out two random notes on a guitar neck.

So, my question is, does anyone have some tips for how to do this quickly? I can pick out the actual interval pretty much instantly, just not whether it's major, minor, augmented, etc. When I want to figure that out I usually have to visualize a guitar neck. Is there a shortcut for this so that I don't have to visualize anything other than what's in front of me and I don't have to count every semitone to figure out if it's minor or whatever? Any help would be appreciated as I've found nothing after scouring the net for a couple days.

This is a pretty odd question, since you say you can easily identify intervals but not their tonality. All I can say is that you have to put those notes in context of the key signature - I think that when I look at scores, I constantly have the key-signature in my head, and when I come across an interval, my brain follows these steps:

1. Identify the bottom note
2. Identify the interval
3. Look for accidentals.

So if I was in C, I would come across an E with a third on top and no accidentals. Then I would know that because E natural to G natural is minor, it's a minor interval. But I guess the problem you are talking about is that you wouldn't immediately know that particular intervals are major or minor. I would have to say that the reason I can instantly tell whether or not an interval is minor or major is because I'm a pianist, and it's fairly easy to see how many notes there are in between intervals on the piano, and that gets ingrained in your head after you play the piano for a while. I've never played guitar, but I would imagine that playing the guitar would have the same interval-ingraining effect (because guitar players have frets.) I guess what I'm saying is that the way to learn the tonality of an interval is just memorization.

Now of course, if there is a sharp on top of the interval, or a natural where there was before a flat, it's likely that the interval is major or augmented. If there is a flat on the bottom of the interval or natural where there was a sharp, then it's likely the interval is major or augmented. But if there is a flat on top of an interval or natural where there was a sharp, or there is a sharp on the bottom of a interval or a natural where there was a flat, then it's likely the interval is minor or diminished.

Really, just learn your scales.

Recognize what scale you're in, what degree your going to and what (if at all) is the alteration.

...

I'm very comfortable with a variety of scales and modes actually. Maybe I just don't fully understand how keeping the scale at any point in the piece in my head would help me quickly identify the interval. For instance, if a melody is using the C major scale and it plays the a D followed by a B I would notice that those are the 2nd and 7th degrees of the scale but that doesn't imply to me major or minor. I'd have to count semitones or visualize where those two notes would be on a guitar neck still.

Maybe I'm just expecting patterns where memorization is simply easier. When playing guitar it's immensely easier to memorize patterns instead of actual notes as every pattern can be moved up and down the neck for easy transposition.

I think your method with visualising a guitar isn't too bad. Like Dan Gilbert I come from the piano, so I always automatically see a piano keyboard when I read intervals and it becomes instantly clear what inverval it is. The guitar has the downside that it's not quite as visually simple as a piano keyboard (which has the advantage of looking the same in every octave), but I think with practice you can do that quite as well on the guitar. But with time you will also internalise the five-line note system to such a degree that you immediately can read an interval by considering how many semitone steps lie between them, diatonically, while leaving out sharps and flats first:

No semitone step: maj. 2nd, maj. 3rd, aug. 4th
One semitone step: min. 2nd, min. 3rd, nat. 4th, nat. 5th, maj. 6th, maj. 7th
Two semitone steps: dim. 5th, min. 6th, min. 7th

Then augment the interval by a step for any sharp on the upper note or flat on the lower note, and diminish it for sharps on the lower note and flats on the upper note. (Natural signs can count as either "sharps" or "flats" depending on they key signatures.) For example, in C-major you'd directly see about the interval Bb-D that between the two "noteheads" B and D there is one semitone step which would make it a minor third, but you then increase this interval by one because of the flat on the lower note, making it at major third.

I don't think however that this method will be faster than your guitar-visualisation, so just use what works and use it over and over again till you're fast. After enough time you will have seen, say, the interval F-B so often that you instantly translate this note-image into "diminished fourth". The method of getting there doesn't matter a lot in the end.

If you know all the major key signatures, you can use them to identify intervals. Example:

I see the interval A-C, and recognize that it's a third. I know that the key of A has a C# in it, so a major third up from A is C#. Since our interval is a half step smaller, this must be a minor third.

The only way this doesn't work is if the bottom note doesn't have a key signature (for example, A#). In this case you should remove the accidental from the bottom note and change the top note accordingly. For example, if I had the interval A# to CX, I would lower both notes a half step, ending up with A and C#, which we know is a major third. With a bit of practice, you'll start recognizing intervals without going through the whole process.