Countermark

https://rpc.ashmus.ox.ac.uk/countermark/915 
GIC 794
denominational mark Δ
circular 
7.5 mm 
Δ has short serifs at each corner; sometimes on reverse 

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC VI, 4401 (temporary) Show 3999 5 6
RPC X, — (number not assigned), type ID 86723 Show 1728 5 10
RPC X, — (number not assigned), type ID 59742 Show 1577 1 10
RPC X, — (number not assigned), type ID 60916 Show 1776 4 10
RPC VIII, — (number not assigned), type ID 20318 Show 1110 7 8