Hi Phew, that is a very old symbol, so there are many ways of saying it If they are used as fencing in the UK - a row of linked upright iron bars with arrow heads - they are often called spiked railings But you may have to tell us more about the context you want Dave
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dave_anon A spike on some railing doesn't really doI agree that it has to be a bit fancier than merely a tapering to a point, but I was following from the original post that talked of "arrowheads". To my mind, there is no problem with an arrowhead design on top of a railing being called a "finial".