Some of my favorite mystery paintings

Here are four of my favorite mystery paintings. I have tried unsuccessfully to identify the artists over the past decade, or more, but probably never will.

12" x 16" watercolor on very fine rag paper, unsigned, inscribed verso "Key West watercolors, Back Street". "YKK" is written very faintly under the mat in the lower right corner. Possibly artist's initials. Probably dates to the late 1950s to mid-1960s.

7" x 10" watercolor on paper, possibly signed in pencil but too faint to read. French, I think.

20" x 28" oil on cardboard, unsigned. Painted 1912-1915 when the Riga (Latvia) Art School was temporarily housed in this building. Possibly the work of a Russian student at the art school. I paid very little for this in an auction on ebay, when it was first offered, one of the first in a group of paintings by this artist. Very quickly bidding became spirited on the other works and they sold in the high hundreds to low thousands. This painting was one of the best in the lot, I think. I think some collectors or resellers may have identified the artist, though the works all stand on their own merit.

8" x 10" oil on Masonite panel, unsigned, from the estate of a local couple. This hangs in my kitchen.