Masons’ marks were used to indicate which mason had worked which piece of stone, probably as a way of allowing them to be paid accordingly.
It is clear that not all pieces of stone were identified in this way, and there is evidence to suggest that in some cases, at least, this was due to varying methods of payment dependent on the type of masonry work undertaken.
The designs of masons’ marks tend to be quite simple, involving a series of straight lines, but occasionally curved elements. This gave them the advantage of being produced with the minimum of effort whilst still being distinctive. Masons’ marks can be located just about anywhere in a church, including, unlike general graffiti, high up on the stonework, out of normal reach.
Frustratingly for us, masons’ marks can include symbols that are also commonly found as apotropaic marks, such as conjoined V’s or a W, or a pentangle. A distinguishing trait is that a mason’s mark would have been carved or stabbed in with a chisel or punch and may be fairly neatly executed. Also, you may find several examples of a mason’s mark that look very similar – i.e. all done by the same hand.
On wood you may find carpenters’ marks, which are not individual to the carpenter, but relate to the assembly of the structure. These often take the form of Roman numerals, neatly carved.
Masons’ marks and carpenters’ marks are not graffiti in the same sense as other marks, but we record them.