Harley Quinn's legal parole documentation gives her name as "Harley Quinn." But this is a legal system document which would be under a person's real name, not their alias. It should have said "Harleen Quinzell."
When Batman and Robin are chasing Harley Quinn, Batman stops at a stoplight. The light turns blue, not green, to signal him to go.
When Harley and Veronica back away from the Batmobile, the marquee above the Bijou reads, "A Porus Line." This appears to be a misspelled pun on "A Chorus Line."