Countermark

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

Coins with this countermark

Number Image TypeNumber CoinNumber VolumeNumber
RPC VI, 4401 (temporary) Show 3975 5 6
RPC X, — (number not assigned), type ID 86723 Show 1516 5 10
RPC X, — (number not assigned), type ID 59742 Show 1570 1 10
RPC X, — (number not assigned), type ID 60916 Show 1754 4 10
RPC VIII, — (number not assigned), type ID 20318 Show 1107 7 8