This is the potters mark of Annie Horsley, an American born artist now living in the UK.
"She studied art at Rhode Island College, later switching to nursing in England before dropping out. She later married but soon parted from her husband. After a hippy life around England — with a spell as a life model — she moved to Pembrokeshire and sold pottery. She met her current husband Phil in Cumbria and they set up home on a narrow boat near Oxford and then Ellesmere, Oswestry. They had two daughters, Rosie and Mollie, and joined a creative community in Scotland. It was then that she saw their present home in Llangwnnadl advertised in a paper as “a naturalist’s retreat."
I’m pretty sure it’s one of many stylistic variations of marks used by Andrew Hague (1948-present) of the Askrigg Pottery in Leyburn, North Yorkshire. Note the dot between the legs of the superimposed AH mark, which is also seen on the posted vase. Perhaps Hague added that to differentiate his mark. A couple of examples for Hague shown below.