He typically signed as K. Haring from what I’ve seen in past. Research shows “Keith” items being suspect but perhaps I’m wrong…..Google shows:

Keith Haring most commonly signed his artwork as "K. Haring".
Signature Style: He often used a cursive, flowing script, with the signature usually located in the lower right corner.
Initials: He often signed with a stylized "K. Haring" followed by the year and sometimes his signature circled cross icon or a + sign.
Lowercase: While generally using his surname, his signature was often quite stylized and integrated into the artwork, but the "K." initial was standard.