Yes.

It usually looks like this:
http://www.hotrodders.com/forum/attachment.php?attachmentid=18402
There are minor variations of that mark, but it's roughly the same on most anything. Snowflake with a W inside it.

Also look here for more info. The Winters mark is a big deal to alot of GM guys because they did tons of casting for GM (as well as others), and in general have a great reputation...

DF with a backwards "D" and interlocking "BB" are other common foundry marks