Bayard was a brand name for Henri Pieper guns.

The Bayard name comes from the street in Liege on which Pieper had their original store. In fact, Bayard is a legend. The brand name was used when Nicolas took over his father's business. The Bayard trade name was used from about 1910 until Pieper closed their doors in 1957.
Your gun looks much like my Bayard 28ga from 1947:

A clearer picture of the flats and water table would help date it. You can find the proof marks and date codes here:
http://damascus-barrels.com/Belgian_All_Proofmarks.htmlPete