I have 2 World War I "dog tags", one each from two different soldiers, which provides name, DOB and some regimental info. One of them I think may include some address information. Is there any way I can research these individuals? Ultimately, if they've any living relatives, I would like to return these tags to them. Any ideas?
I would contact Volksbund, an organization that takes care of German war graves, and Deutsche Dienststelle (WASt), a federal organization maintaining records on servicemen, and ask if it helps to return these tags to them (especially WASt) and provide as much details on the provenance of these tags as possible. They might answer requests based on these information somewhen in the future. Please see their site Erkennungsmarkenverzeichnis/Verlustunterlagen, they write:
Sämtliche der WASt zugehenden Erkennungsmarken werden nach erfolgter Registrierung zwecks eventuell späterer Herausgabe an die Angehörigen gesondert im Ref. II B aufbewahrt. (All dog tags given to the WASt are registered and stored for a possible return to family members)
You should also take good quality photos of these items and put them permanently online (e.g. Flickr) with a transcription to help public research. Privacy is not an issue here, given that the soldiers where born in the 19th century.
What I would not do (I am not assuming that this is an option for you, but want to mention it anyway): Please don't make them commercially available, as this market fuels illegal grave digging, the destruction of grave sites and often destroys the last chance of giving a dead body a name.
Please check my answer on How to find information on German soldiers from World War I and World War II? on the (limited) research possibilities regarding German participants of World War I.