Good point, Michael.
Indeed, it's not as simple as 29.97 and 30. I was forgetting that I'm on an FCP forum and not an After Effects forum (In AE, 29.97 fps is always drop and 30 fps is always non-drop when you're in the Composition Settings panel). Even though the .03 difference between 29.97 and 30 is meant to account for the time that's gained by dropping frames, this is not consistently followed.
So, you could be in an application and have "29.97 drop" and/or "29.97 non-drop" and then in another application and have "30 drop" and "30 non-drop".
One should always look for the visual indicators (as Michael mentioned), like a semi-colon (";") for drop and colon for ":" drop. On video hardware (like a camcorder or deck), it's likely to take the form of a period (".") for drop and colon (":") for non-drop, but even there might no indicator difference. You might just see ":". It largely depends on whether it's pro hardware or consumer hardware.
Perhaps most importantly, if you're not sure then visually inspect the time code. If at minute one you go from 0:00:59;29 to 0:01:00;02, then you're using drop frame time code. But if you go from 0:00:59:29 to 0:01:00:00, then you're using non-drop. This skip from ;29 to ;02 would present itself very minute except for a tenth minute.
An of course, this is only applies to SMTPE time code. QuickTime's inspector window reports in 1/100 ths for the frame count. Unless there's a Time Code Track embedded in the file, you're looking at numbers like 05:02:22:33.334 instead of 05:02:22:10.
Fun, fun.
-Warren