Every Montessori classroom has these suction cup pads out on their practical life shelves at one time of year or another. They can be a bit hard to find and I totally scored when I came across these! I think they are made to be a bath toy as they are flat on the other side so they'd be for a child to make shapes out of...similar to tangrams.
They are great to use with water, beads, or pom pom balls as these cups are a bit bigger than the average so they are a bit more diverse!
I love putting a few of the basic shaped ones out at the beginning of the year with color coded pom pom balls.
I believe you can find the classic white circle ones at Amazon (I've had good luck finding these at garage sales) and you can get shaped ones (ducks,dolphins, etc) in the bath section at Fred Meyer. Although you have to buy a pack of eight...all the same...but then your friends will love you because you can share!