Hi AJY, welcome. And thanks for the additional images.
I have taken the opportunity to invert and enlarge the central section of the image to get a better understanding of the possible "Ca".
At fist I thought it could just be a poorly formed "P", but no. Then I thought it might be a "light bulb". In the enlargement below it does look like "Ca".
It is clearly not one of the weights that included a "date letter" (A thru Z).
Is the base of those weights a colour ground or just clear glass? And how is the base finished - unpolished or flat polished or concave polished? Is there a "P" cane in the base?