What I did it was the only way to keep the bike fairly original. Whoever owned the frame before me must have used it on a trainer, it had many rust spots under the hurry up paint job I originally did. Under the top tube, on the seat tube- nasty. It was really beyond simple touch up.
New paint wouldn't be that expensive as I know some guys in a body shop.
I wanted a different color, but couldn't find any decals.

Edit: It looks deceptively good in that photo.