A curious initial

[FLITZ]

Recently whilst doing a disco for a party at a house nr Halifax I came across what appeared to be a door or window lintel out in the garden, and yes I am aware this is the secret Leeds web site, but this intrigued me so much as the lintel had carved above it the letter D then in a carved square the date 1620 then the letter H, it was a heavy stone lintel and was very old, the house in question was called Cliffe Hill East and I believe it was part of an old coaching house, it's situated on the A649 nr the village of Lydgate nr Brighouse, can anyone enlighten me or the owner as to the significance of the carved letters or the date.