How about the sun hits, the black lettering gets hotter than the white, melts that portion more... to produce that effect.if it is an embossed it would be real
It all happened in Mustang Oklahoma after an ice storm... its real and happened on multiple signs.
It is forming to the vinyl layers on the signs.
I doubt they were embossed. All the clients I have who produce roadsigns use layers of vinyl. There's the reflective base signs and then the lettering itself. I have no problem believing the ice adhered to the sign, conformed itself to the vinyl layers, then melted from the sign heating underneath it and slipping off.