It certainly looks Polish but my Polish website doesn't recognise it. It does have Westerowski and Wystrychowski as extant surnames in Poland. Strange thing, if you google this name for Polish language references exclusively you get two hits; if you google for German language references you get 165. In addition the Polish references to a Westerkowski are in a German document where it's among a lot of German names. Assuming the name is Polish it appears to be rare, and to belong to a part of Poland that was subject to German or Austrian control. The Westerkowskis may have considered themselves German rather than Polish, and relocated to Germany after World War II. I assume the meaning is locative.