I had been previously unfamiliar with the Spesmilo symbol. It apparently was only used on a single 'coin', a 1912 fantasy issue of the Esperanto congress. (The NGC web site lists examples in MS60 and XF40). According to Wikipedia the coin was used before the first world war by a few British and Swiss banks
Unicode has assigned the symbol U+20B7 SPESMILO SIGN.
The denomination was planned to equal 0.8g of 22k gold, or about 1/2 a US dollar, 2 shillings in Britain, or one Russian Ruble. It was supposed to be worth 1000 spesmiloj. The denomination is obsolete: Esperanto fantasies struck after 1945 are based on the imaginary Stelo system, not the Spesmilo.
On the Mac if I try to enter the Spesmilo sign I do NOT see the expected Sm abbreviation. Instead I see a P with a line through it. I have pasted it here: ₷. I have no idea what you will see. It is supposed to look like this:
The P with a line through it is the new currency symbol for the Russian Ruble. Microsoft has apparently rolled out support for the new Symbol in Windows. The Mac, at least mine running 10.8.5, has placed that glyph at the code point for the Spesmilo sign ... a denomination equal to one ruble.