Not sure TBH, just know it was common slang. Most often heard it referred to WRT a 'ten bob note' (no s, bob was both singular and plural.) 

Craziest thing is to think there was a note worth 50p in todays money (1/20 of a £ but there were 12 pennies to a shilling) that you could buy a shit ton of groceries with! 

 I more recently came up with a symbol for my bobs idea too 🤣

Bits n bobs. Bitcoins and bobcoins. Please send bobs.

https://pbs.twimg.com/media/FgY1SXwWYAAmeOS?format=jpg&name=large