August 5 was a big day for sports births (a long list)...

[Shampoobra]

5. I only saw the back of it, but...

...it was black with stark white lettering (the "8/5/1980" message).

Edited to add:

I mentioned up-thread that he looked like he could be 33, which would be consistent with the inscribed date being his birth date. So I did see his face and a glimpse of the front of the cap, and I remember the cap's visor having a gold emblem of some kind. This is the Seattle area, and I don't know of any local teams with black and gold colors.