Medailonky s Mucha motivy

Seen on a billboard: Medailonky s Mucha motivy. Translation: medallions with Mucha('s) motifs. The problem is that that is English, not Czech syntax. And it's not the first time I've seen it. In real/proper Czech, Mucha would have to be in the possessive adjective case, which would give us Medailonky s Muchovými motivy, or at least in the adjectival form: Medailonky s muchovskými motivy. I've even heard on occasion constructions like Medailonky s Muchy motivy (in colloquial Czech motivama), with Mucha in the genitive case, but Mucha in the nominative just isn't right.