A signal is not the same thing as a guarantee. Both of your points so far, i.e. your provided text & that bots often bother to replace em dashes to avoid detection, actually support that it is a signal though.

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Retr0id 2 hours ago | parent [-]

The stronger signal is the grammatical structure, not the specific glyph used.

	▲	zamadatix 2 hours ago \| parent [-]
		The stronger yet signal is both combined! This glyph, that emoji, a given sentence structure, that formatting, a certain phrase. The more you notice -> the stronger the signal, the more you miss/discard -> the weaker the signal.