'Alana' LAV419
is a beautiful mermaid stamp from Lavinia Stamps. I can imagine the lower part of her being masked off and stamped so that she appears to be emerging from the water.
This is a clear stamp.

It measures approx: 10 cm x 3 cm (measuring across her outreached hand, nearly 5 cm across her tail).
Or, 4 1/4" x 1 1/4".