For some, a simple 'x' will do, but if you want to write something a little more imaginative (particularly if your card is fairly minimalist in design like the red and gold foil one below) we've got a few suggestions...
"Nunc scio quid sit amor" - latin for "Now I know what love is". Beautifully simple.
“The best love is the kind that awakens the soul and makes us reach for more, that plants a fire in our hearts and brings peace to our minds, and that’s what you’ve given me.”
A quote for film fans from The Notebook
You could go classical with this stanza from English poet Lord Byron's 'She Walks in Beauty'
She walks in beauty, like the night
Of cloudless climes and starry skies;
And all that’s best of dark and bright
Meet in her aspect and her eyes;
Thus mellowed to that tender light
Which heaven to gaudy day denies.
Or perhaps something from the 'Bard of Avon' himself - William Shakespeare. A heartfelt sentiment from 'Romeo & Juliet'
My bounty is as boundless as the sea,
My love as deep; the more I give to thee,
The more I have, for both are infinite.
Or modern with punk poet John Cooper Clarke's 'I Wanna Be Yours'
I wanna be your vacuum cleaner
breathing in your dust
I wanna be your Ford Cortina
I will never rust
If you like your coffee hot
let me be your coffee pot
You call the shots
I wanna be yours
If the thought of writing a poem brings you out in hives, you could opt for some of the worst / confusing / nonsensical lyrics in pop history, which at least will you give you plenty to talk about when the card is opened.
I want you all to myself. You’re metaphorical gin and juice.
We spinning on a roller coaster. A free fallin’ into your yum yum.
I feel like love is in the kitchen with a culinary eye. I think he's making something special and I'm smart enough to try.
Oh babe, I wanna put my log in your fireplace.
Girl you look just like my car, I wanna wax it.
We could go on with these, but let's finish with Shakira's, “Lucky that my breasts are small and humble, so you don’t confuse them with mountains.”
Thankfully many of our Valentine cards do all the hard work for you.
And then a simple 'x' will most certainly do.