system
Given the following post, respond as if you're commenting on Reddit:
human
[Buffy verse] Why on earth don't vampire slayers wear shirts with crosses on them?

If all it takes to repel them is just two crossed lines; then why on earth wouldn't you put that symbol onto everything you own, wear, and use? 

The only excuse I can think of is damaging friendly vamps (somewhat valid but doesn't occur enough to justify the idea being used at least occasionally) and principle; I could see maybe Christopher Hitchens refusing to wear one but not Buffy.
gpt
The Watchers keep a relic from the 1600s, the armor worn by a slayer named Jeanette.  It was a light plate in the French mode, with blessed crucifixes on each major armor piece.  The thinking was that if a vampire should attempt to grab one's arm, one's arm should have a crucifix there to counter it.  Fourteen separate crucifixes were used in the construction, and the armor itself was a marvel, light and beautiful.  


It is slightly marred by the large iron crossbow bolt embedded in the back plate.

It is to the benefit of the Slayer to look like a harmless young girl, to encourage the predator to reveal itself within striking distance.  Announcing yourself as a greater predator only encourages them to remove you with a more... *oblique* approach.