TL;DR: Are there shorter, established notations for the sine function and other trigonometric functions than "$ \sin(x) $" etc.?

In a some homeworks and tests, there are exercises (e.g. differential equations or matrices) which contains sine and cosine, which I have to write very often - obviously, this becomes quite annoying. 

My usual "workaround" is, that I define $ \sin(x) = s $ and $ \cos(x) = c $ to safe me from writing the rest and loose time unessecarily. As far as I can see, this is totally correct and can't be marked as wrong.

Yet this reduces the readability (and probably annoys the corrector). So are there any shorter notations for the trigonometric functions, which are established or at least sometimes used?