Topps was very, very good at following up their jobber and constantly pushing them to move product. One way they did this was to use a penny postcard to send a stream of reminders. This one is from the wilds of the WWW and is for Stop 'n Go gum, so it pertains to to either the small, 1949 and/or larger 1950 version of the gum that was sold along with the License Plates cards. It's in rough shape but that's probably due to the real cheap stock used:
They certainly grabbed your attention from the first word, those Topps boys did! The use of the word novelty may lean toward this being for the earlier issue but it's really no smoking gun. The front shows this card was never used:
A simple penny postcard was a vital tool in the early days. By 1952 the rate had gone to two cents, so I wonder if Topps changed methods or just went along with the bump.