These were locally printed, temporary proprietary tax stamps used by St. Louis druggists immediately after the War Revenue Act took effect on July 1, 1898.
The federal government had not yet delivered enough official proprietary stamps, and small manufacturers couldn’t halt production. So, several St. Louis firms created their own provisional stamps—with the tacit approval of local revenue officials—until proper federal supplies arrived.

St. Louis was a major pharmaceutical and patent‑medicine center in the 1890s. When the new tax hit: Federal proprietary stamps were delayed in reaching the Midwest, local druggists had inventory ready to ship and couldn’t legally sell without tax payment, and the IRS allowed temporary solutions as long as the tax was clearly indicated and records were kept.

Thus, St. Louis became one of the two cities, the other being Macon, GA, where firms issued provisional proprietary stamps. Most of these were used for only a few weeks, generally July–August 1898, until official proprietary stamps arrived from Washington. Because of this short window, genuine used examples are scarce, and on‑product or on‑wrapper examples are especially desirable. 

Catalog Values on these provisionals range from a $125 for the imperf Meyers Brothers Drug Co up to $25,000 for several of the others.

They represent a unique local adaptation to a national tax law—exactly the kind of story that makes a thematic exhibit come alive.