What would you like to know about that poster stamp? I see that they are sold on private web sites for $10 to $13 (asking price, not necessarily selling price).
It's certainly a colorful stamp. It was based upon this poster promoting the same event:

For more reading on the event, check this out from the Pan Am Union (Vol. 44):

Finally, if you look closely at the bottom of the stamp you scanned, there the name of the printer is New-Art Lithographic Co., New York. They weren't around too long, as it seems they filed for bankruptcy in November of 1917 as per this NY Times newspaper article:
