Rolf Harris reportedly sent the card to one alleged victim - a childhood friend of his daughter Bindi - who claims he had been abusing her for years since she was age 13.
On the cover is a picture of a dog, alongside the words: "All I need to know about life I learned from my dog.
"If you stare at someone long enough, eventually you get what you want. When it comes to having sex, if at first you don't succeed, beg.
"Always give people a friendly greeting, a cold nose in the crotch is effective."
According to The Mirror's court reporters, the inside of the card reads: "I hope this info is all true.
"I've just had a dreary bout of vertigo with the inside of my head seeming to spin ceaselessly in an outer bony shell of a head which never moved as I fell sideways against the wall like a drunk.
"See you soon love Rolf."
The strange message, the meaning of which was not explained in court, was accompanied by a few cartoons penned by the former Animal Hospital presenter.
The woman, now in her late 40s, told jurors at Southwark crown court that she thought the card - sent to her while she was in her mid-20s - was "vulgar" and "rude".
She reportedly told jurors: "It was a card that was a bit disgusting.
"It had a very sexual tone to it because of the sexual content I felt it had."
Rolf Harris, 84, denies abusing the girl but admits having a sexual relationship with her after she turned 18.
The trial continues.