I *think* it was added in the late '90s along with the rest of the mess that was done to that building. It's falling apart and doesn't belong there, hopefully the new owner (UMN) will remove it.
FWIW, it looks like the original lettering was done with stucco, which is pretty weird and clever.
Interesting, wonder if we'd get an answer. In the meantime I just learned there was *another* GRODNIK downtown on S 6th Street. Were there even more? 🤔
In 1958, they were promoting - via want ad - the 2nd floor business on 6th that shows up in Vince's photo.
(Check out the ad for Doris in the right-hand column. She'll type anything, almost.)