The Art Gallery of Ontario in Toronto, Canada, maintains a reference library (including an artists archive) as well, which is open to the public. The library uses this simple stamp, quite often with an ink (as here) which does not fit well with the special paper used in art publications.
The stamp itself is a circle, highlighting not the name of the Gallery (which is used as corona), but of the library. The meaning of the star at the bottom of the stamp is not apparent.
Besides the round ink stamp, the library contains books from other libraries, which used other stamps, like this embosser.