The Montreal Museum of Fine Arts is a pretty quiet place nowadays. It seems that a light fingered Louis, had off with this relief of a 5th century BC Persian Guard. The museum takes pride in allowing viewers low level security so that they can get up close to observe their collection.
The thief was captured by security video. He is about 5'7". He wore blue jeans and a black jacket, and was a he, of course, and he wore a baseball cap (no doubt backwards).
If you happen to find this work on a sink in a public washroom, or on a bus seat (not very likely though), give the museum a call. They will welcome you with open arms.