What do you want to say?  Where on the garment would you like it? How many slogans?

Most garments have 4 potential locations.  Believe it or not these are:

The front

The back

The right sleeve

The left sleeve

You could also subdivide the front into left and right if you think it would work.

If you needed any of that explained to you then you will probably choose a vest.  In which case please do not ask for anything on the sleeve!  If you do there may well be a sloganism designed especially for you.