Triskelion
The name of the triskelion means “three-legs” in Greek, and is a synonym to trapeza, which also means “banking”, because in ancient times a banker’s table had 3 legs. If the triskelion symbol is a synonym pun, then it perhaps simply stands for “banking”.
There may also be homonymity puns involved here. Possible spooky meanings are Latin tric / scelus for “tricks & wickedness”, or Greek ateros / gelon for “mischief & mockery”. This doesn’t match the triskelion usage very well though, so more research is needed.
One prominent use which I can explain is the flag of Sicily. The flag itself is called Trinacria “three-ends”, because the island Sicily is a triangle. It features several triskelion themed puns: the τρι-σκελος tri-skelos “three legs” themselves (naked here), and also 3 corn husks around a gorgon’s head. The gorgon may stand for the phrase αθρησειε κηλειν athreseie kelein “bewitching gaze”. The husks may stand for the phrase αθηρ σκολιον ather skolion “wound corn husks”. Both Greek phrases are near-homonymous to triskelion, though that is not apparent, probably not even to Sicilians. Oddly, the corn husks were officially added in te 1940s, but the pun only seems to work in Ancient Greek. In Sicily’s case, the triskelion really seems to stand mostly for the island’s triangular shape. Ancient Syracuse was of course also a financial hub, connected to Roma and Carthage.
The Isle of Man flag also has a triskelion, even though the island isn’t a triangle. It may be connected to Sicily through imperial spook families. On the Isle of Man, the triskelion legs have armor & spurs, which I assume are again important for some wordplay, perhaps with spurious. The local Manx name is said to be ny tree cassyn “the three legs”, perhaps for a localized pun with tricksing.
As for the many swirls and other triangular symbols that are lumped in with the triskelion, I’d say that they have different origins & meanings: A true triskelion would need thee legs, because that’s what the name means.
Greek tri-skelos = three legs
triskeles : a symbol consisting of three spirals, or three bent human legs; from Ancient Greek τρισκελής (triskelḗs, “three-legged”), composed of τρι- (tri-, “three”) + σκέλος (skélos, “leg”). — English (Wikt)
Greek trapeza = three-legged table, banker
τράπεζα trápeza : a table; From Proto-Indo-European *tr̥-ped-ih₂- (“having three feet”), from *tr̥- (“three”, combining form) + *pṓds (“foot”). — Ancient Greek (Wikt)
τραπεζίτης trapezités : a money-changer, banker; money-broker; exchanger — Ancient Greek (Strong)
τραπεζίτης trapezítis : banker, bank owner or shareholder — Greek (Wikt)
Greek athreseie kelein = bewitching gaze; ather skolion = wound corn husks
ἀθρέω ; ἀθρήσειε athreo; athreseie : gaze at, observe; inspect; watch; look upon; perceive — Ancient Greek (LSJ.gr)
κηλεῖν kelein : bewitch, calm, charm, enchant, soothe, soothe charm — Ancient Greek (LSJ.gr)
ἀθήρ ather : an ear of corn; husks, chaff; awn — Ancient Greek (LSJ.gr)
σκολιός ; σκολιόν skolios; skolion : curved, winding, twisted, tangled; crooked; bent — Ancient Greek (LSJ.gr)