did you know that Photoshop now lets you make signed distance fields for great reduction in your decal mask sizes? 
(here are the two images I'm using for above, they're 64x64 but blown up so you can see the pixel detail)
the way you do it is to make a document in HD size (1024 or 2048 are good) and have your decal on a separate layer
then add a stroke layer style to your decal layer set to gradient and "shape burst"
flatten this, resize bicubic down (64x64 can work, 128 or 256 will be better if the decal has finer details) and then import into your game engine as a linear greyscale image
flatten this, resize bicubic down (64x64 can work, 128 or 256 will be better if the decal has finer details) and then import into your game engine as a linear greyscale image
examples for how scale affects the output or e.g. if you had texture mip settings for a PC game
A, B - you'll get better corners at higher resolutions (128 SDF vs 128 bw mask)
C, D - and it's still functional at lower res, but shapes start to break down (still an improvement!)
A, B - you'll get better corners at higher resolutions (128 SDF vs 128 bw mask)
C, D - and it's still functional at lower res, but shapes start to break down (still an improvement!)
