Hello there,
while browsing the internet for historical material for the 17th century I stumbled upon something rather peculiar. In a few depictions of duelists and and fencing teachers of the 17th and 18th century they are wearing doublets or jerkins with a heart-shaped patch applied. After a few search attempts I couldn't find any information about this and would be glad if someone of you could help me out.
One picture I found shows Jean Béraud (although this is from the 19th century): https://i.pinimg.com/originals/43/9e/72/439e72f23a7f4a44dc932c87a4acfdf6.jpg
I also found a video of the Sieniawsk Fencing School in Poland that recreates mostly (?) 17th and 18th century fencing styles. The teacher in this video wears such a jerkin: https://www.youtube.com/watch?v=qcbrLPtEDDI
Thomas Stephens mentions the heart as a part of the uniform for fencers at fencing schools. From a New System of Broad and Small Sword Exercise (1843):
“An easy dress should be worn, and it is usual, in academies, to have a spot or heart on the left side of the breast of the waistcoat.”
Other references says it was worn only (or mostly) by fencing masters. Why is a little more unclear - it seems likely it was used as a badge of rank for the mastersb as well as an instructional aid that gave students a target.