What Kind Of Swiss Stamp Is This?

This stamp looks very similar to the official Swiss stamps of 1910. However, unlike those stamps, this stamp is numbered - I have two of them and each has a different number - and the numeral is surrounded on both sides by the letter 'P,' which is not the case with the official stamps, which just have the numeral.

This is probably the first individually-numbered stamp I've come across, so I'm very curious as to what it is. Does anyone know?

They are called Franchise stamps and are listed in the very back of pages of Switzerland of Scott's. They were used by charitable societies and other institutions for franking.

This is listed in SG (Simplified) after the postal stamps, under the heading: Frank stamps. Issued to charity hospitals for transmission of their mails. 1911. With control figures at top. Your stamp is SG F273.

Most interesting!

Thanks for the help, guys.