What the sources claim for it
Passage between things. Speed, exchange and the crossing of boundaries.
History
Where does Mercury come from?
The sign combines the horned cap and the staff of Hermes, and the metal it names is the only one liquid at room temperature. That fit was not lost on anyone: quicksilver is mobile, it carries other metals into amalgam, it is a messenger and a go-between, and the planet is the fastest of the seven and never far from the sun.
Its operations are communication, commerce, thieving, eloquence and knowledge — the same portfolio the Greek god carries, transmitted through the Roman one into the grimoires, where Wednesday's hours are given to writing and speech.
1 figure
Who is it attached to?
Figures who carry it
An attribute rather than a signature — held, worn or associated in the texts and the images.
Afterwards
What did it turn into?
Astronomical notation for the planet, the historical chemical sign for mercury, and still in use as a hazard mark for mercury compounds in some contexts.
Which texts describe it?
Oldest first, with what each one does with the mark. A mark described in a Bronze Age incantation and a mark first drawn in a seventeenth-century manuscript are different kinds of claim, whatever the shape has in common.
Renaissance & Early-Modern Occult Angelology
Agrippa, Barrett, and their compilers · 16th-19th c. · Latin and English
The mercurial square and its hours.
Read Renaissance & Early-Modern Occult Angelology in full ↗Cover: Public domain · Otto Rietmann · Wikimedia file page
The Key of Solomon (Clavicula Salomonis)
Anonymous; ed. S. L. MacGregor Mathers · 15th-16th c. · Latin and Italian
Pentacles of Mercury for eloquence, knowledge and business, made in mixed metal.
Read The Key of Solomon (Clavicula Salomonis) in full ↗Cover: Public domain · Unknown author · Wikimedia file page
Nearby
Related marks
Saturn
The scythe. Slowest planet, heaviest metal, and the authority a grimoire invokes for work involving binding, decay and the dead.
Jupiter
A stylised Greek zeta for Zeus. The sign of increase, favour and judgment in one's favour — the grimoires' preferred authority for asking.
Mars
Shield and spear, iron, Tuesday — and, since Linnaeus, the biological sign for male, which is a much later and quite separate job.
The Sun
A circle with a point at its centre — the oldest form in the set, and the one the alchemists used for gold without further explanation.
Venus
Copper, Friday, and every operation to do with love and favour — the counterpart to Mars in the grimoires long before it was in biology.
The Moon
A crescent, silver, Monday — the planetary authority for anything involving dreams, water, change and things done at night.