An one-signed phrase used mostly by ASL speakers, who don't mean true love. It means more like: "you're great!", "I like you", "I care about you", nothing more.
This sign with the ILY handshape is a verb (LOVE-YA). It's used, instead of signing "I LOVE YOU" to make clear it is not for "real".
Example: "I had a lot of fun hanging out with you. Love ya!"
But, a subtle difference of movement in different contexts can convey a different mean. E.g. WAVE-ILY can mean a friendly farewell "hug" with a close friend.
Or, it can mean an abbreviation for "I LOVE YOU" during farewell between a child and her/his parent.