Sacrum:

"He was a great friend of Charles Cotton of Beresford Hall, who built a fine fishing-house near the famous Pike Pool on the River Dove, over the arched doorway of which he placed a cipher stone formed with the combined initials of Walton and himself, and inscribed with the words 'Piscatoribus Sacrum.' - the words mean ‘sacred to fishermen’ and are also carved onto the 18th-century fishing temple beside Cromford Bridge.