Does anyone know how to find out about a trademark on antique pewter?

I have some old antique pewter which has been in the house for years,most of it has makers trademarks.What I need to know is,how do I find out who the trademarks belong to,so that I can put a date on the objects,and find out if they have any value.Most of the items are tableware,or just cled as metalware.