The Bell-Towerman’s Keys is a sculpture by Hans Arp.
It normally lives here in the concrete wasteland that is the forecourt of both the Rheingoldhalle and City Hall.
There’s a plaque documenting its temporary absence (and loan to the Arp Museum in Rolandseck, a 100 or so km down river).
The bit about “on loan until October 2012” has been conveniently hidden with adhesive tape.
They said the museum could keep it until Mainz decides what to do with City Hall, a 1973 structure that’s crumbling around the civil servants’ ears.
It might be there for a while.
Ms jb put it rather well.
“If I were a sculpture” she said “I think I’d prefer living here in Rolandseck as well…”
Mainz Daily Photo 
I’ve come back to this post several times, trying to figure out if I like the sculpture or not. As a city fixture, I think not; as you have photographed it, in the wild. . .I’m not sure yet.
It looks very well here! Perfect match with the surrounding.