While it looks like one, I don't believe it is. Most likely a tool chit or something along those lines, or a pole tag. Also while I'm not an expert on fonts, in my opinion, it looks more modern than WWI vintage. That said I could very well be wrong on the font.
Dog tags typically have the individual's name on them, so when remains are found they could be identified by the tag. See below link for WWI dog tag examples.