Many of the ephemeral items produced for Halloween were not marked. Some companies - Dennison comes to mind - were quite disciplined about marking their products, whereas companies like Whitney rarely marked such items, aside from their postcard output. Gibson was a middle of the road firm when it came to marking. One characteristic to look for if you think something might be Gibson is the presence of a slanted exclamation point. Although not a foolproof method of identification, it is a handy one. This particular invitation is one of Gibson's best. The artistry and use of unusual colors make this stand out. These were sold with stock number 1860 during the 1930s.
Mark B. Ledenbach's vintage Halloween collectibles blog.