Mason's marks
Medieval masons all had their own way of marking the stones they worked.
It's not unusual to see them in our ancient cathedrals and religious buildings, but you have to know what to look for.
From the Norman (1066 >) period onwards masons chose any mark they fancied to identify their work, and these marks were often passed down through the family.
Tewkesbury Abbey, very helpfully, has an information sign on one of the pillars (near the entrance) which has several such marks at a low enough level to be seen. Many of them, interestingly, also appear in Gloucester cathedral showing that the same skilled men (or their descendants) were used for such building projects as and when they were needed, wherever they might be.


Mason's mark
Medieval wall-painting
The atmospheric nave
Beautiful vaulting and bosses