A Shell Oil Valentine card.

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The card comes from the large collection of Malcolm Warrington, a council member of the Ephemera Society and its webmaster.

The message did not reveal the identity of the sender. The phrase You can be sure of… at the end must have been a big clue, however.

“Emphasis on anonymity was so strong that ordinary postage stamps were used instead of the company’s franking machine,” he added. “Post-1975, changing attitudes among women customers meant they no longer appreciated being singled out as lady motorists.

“Shell Oil Valentines are uncommon so current prices would be from £25-55 depending on condition and the artist with this one [above] probably in the £25-30 bracket as it’s an attractive piece.”

Vintage Valentine cards are found at fairs and markets across the UK but the biggest selection is likely to crop up at the Ephemera Society’s own biannual fairs in London. The summer event is on Sunday, May 31.