Posted By:
VintageBallNice pick-up! Hammon was one of a bunch of publishers issuing baseball postcards around the same time period (Burke, Taylor, Max Stein are some others).
V.O. Hammon was based in Chicago (I need to double-check this in some of the postcard guides) and issued team cards as well as ballpark postcards.
Prices on the common team cards vary (based on condition, etc.). With some persistence you can find them from as low as around $40 -- with most selling between $80-$125 -- on eBay and elsewhere. I believe Hammon issued some team cards that were oversized, as well (you didn't specify the size of your card).
Here's an example of one of Hammon's ballpark cards, from 1909, depicting the Cubs' home field at West Side Park, where they played from 1893-1915. This field is marked by its rounded 1st base, 3rd base and home pate dirt areas:

For more information on player and team postcards, ballpark postcards and real photo postcards, feel free to visit www.vintageball.com/Postcards.html -- I'll be happy to post your team card in the Player section if you wish (the site currently features scans and photos from a bunch of different baseball collectors).
I hope this info helps and I'll see what I can find in the books on Hammon for you.
--RobertS