[vbezhenar]

Yep, in Kazakhstan almost every government web service uses XML signatures for interoperating. Of course nobody sees it outside of those systems, but it's everywhere inside. I have no idea about other countries, but I would not be surprised to find out that there are many other similar countries or organizations where that stuff works inside. You won't know about it until you touch it.

[cesarb]

Here in Brazil too, for instance the NF-e (electronic "nota fiscal", the English term seems to be "receipt", the documentation is at http://www.nfe.fazenda.gov.br) and the recently released digital payment network (PIX, see https://www.bcb.gov.br/content/estabilidadefinanceira/cedsfn... for the current release of the relevant manual) both use XMLDSig.