The sign in your bio

A sun sign is the sign the sun was standing in on the day you were born. There are twelve, so a sign puts every person on earth into one of twelve boxes.

Dating apps have a slot for it. On Hinge it sits in a short list called My Vitals, after ethnicity, family plans and pets. It is the smallest thing on the page. Once it is switched on, the word does three jobs.

The first is shorthand. It makes a claim about your character without any of the argument that would usually go with it. Nobody writes "I am impatient in the mornings". They write Aries and let the reader fill in the rest. It also gives away a date, because a stranger now knows your birthday falls inside a stretch of about thirty days, and your age is printed above it.

The second is a filter. Bumble puts star sign in its Advanced Filters, which come with a paid subscription. Tinder has an Astrology Mode that works out your signs from your birth details and shows you people it treats as compatible. Filters are quiet. They run on somebody else's phone, before contact, and nobody is told they were removed. Twelve boxes means that ruling out one sign takes away about one person in every twelve you would otherwise see.

The third is an opening line, and it is a good one. Ask a stranger their sign and you always get an answer, and the answer arrives with something to say next attached to it.

Two last facts. The twelve-box system came from newspapers. In 1930 the Sunday Express hired an astrologer called R. H. Naylor, and by 1937 he had a column arranged by the twelve signs, which was as personal as one printed page could be. And the sign these apps show is not the one Indian astrologers use, because the two systems count from different starting points. A profile that says Leo usually belongs to somebody an astrologer at home would call Karka, Cancer.