Australia King George 5th ( KGV usually online auctions) side faces or possibly heads.
I am missing my catalogue right now (not current thouigh) but on
ebay for instance you would find them by the above names. That would hopefully give you an idea of what they can sell for generally speaking.
But . . . they could have errors. That's a good thing or varieties or colour variations, need UV light for some, they fluoresce different colours I think. Also the perfs (perforations) around the edges are different and the watermarks (pressed into paper, look on backs of stamps, change and change value.
Very neat stamp to research and find out about.
Look on Stamp Community here for KGV_Collector's thread on these stamps:
https://goscf.com/t/7020&SearchTerms=kgv