Keys are normally Italy the Vatican but also used otherplaces.
The keys looke exactly like Legnica in Poland (1600 - 1700) however
it is not the same (english word ??) shield in that Polish mark.
I also agree with Regensburg as a possibility, but the Polish mark is even more similar.
Regarding Riga - they used keys.
I think that it looks like one mark. And not two. The shape of the mark with the vertical line op/down - (hope that you can understand this) this shape looks very much like try to visit this link.
http://www.ceebd.co.uk/ceebd/sportsp.htmIt might be totally wrong but that was my first idea before I started looking in my books. A wild guess. Can you se the similarity?