Search for signatures of abstract art on Google images.

Describe the mediums and search Etsy, eBay, Google.

Find local art galleries in your area and ask them, particularly if a consortium of artists who are older.

It's a very distinctive, confident signature, so must be the artist.

I will let you know if I hear back.

I emailed Tromp Percussion Festival - founded in 1970 by Dr. Theo Tromp - with photos of the tiles.

The artistic director, Dominque, replied and said "Cool!" and said he would ask one of the early organizers that he knew.

Then Dominique forwarded this to me:

"What I suspect our American friend has in hand is one of the famed Tromp Delft blue tiles. The Tromp family always had the tradition of giving the jury members a uniquely designed tile for each edition (each edition with a new image). So, collector's items. If I remember correctly, we stopped this in 2010..."