
As the law currently stands anyone( not just Dog Wardens)are required to make all efforts to return an item of permanently marked property(regardless of whether it is a living animal or an inanimate object)to it's legal owner. A tattoo unlike the microchip is permanent & proof of legal ownership.
The OP is simply complying with the law & I suggest contacting the NDTR(which is still in existence)for help as they may be able to suggest which country the tattoo comes from. Also the actual chip number also indicates
the country of origin, I would expect a DW to be aware of this. I would also expect a DW to have checked using
Europet for the microchip registration