Signatures can be very tricky to track down. The usual way to research is by comparing to other signatures either in a reference book or on a website. There is a free artist signature resource on findartinfo.com, and there are several other sites which make a small charge for accessing their collection of signatures and monogrammes. If you think you might have an idea who may have painted your item, you could try looking at auction listing sites for comparison purposes. The liveauctioneers.com website allows you to zoom in on signatures on many of their listings, as does ebay. If, however, you are unable to go any further with your research don't be too shy to seek expert advice from local auctioneers or art dealers.