Take a cotton swab and test the back of the badge with your alcohol or ??? I'd try Goof Off paint remover. Maybe you don't have to get every last bit of it off. Rubbing will remove the crud, but will shine the higher edges of the lettering up. An old badge looks hastily restored when that's done. Soaking might be better. Make some tests on the back to see what loosens the crud up. The paint almost looks fire damaged, or the bike was repainted and spent the rest of it's days up in a hot attic for fifty years.