The maker’s mark is heavily worn, but I am 95% sure now that my anvil is a UAF, made in the town of Feignies in northern France (close to the Belgium border). I found some photos (I’ll attach below) of other UAF anvils which have the same circular maker’s mark.
Cambodia was a French protectorate from the 1860s till the 1950s so it’s not a surprise to find old French anvils here. I’ve found a couple of German ones as well.
UAF (Usines et Aciéries de Feignies) was founded in 1911 but merged with Sambre et Meuse in the 1940s.
http://www.cesari.eu/bricolages/etaux/etaux_histoire_SetM.htm