First, the statute under which Dillon is being charged, Fla. Stat. § 847.011(2), provides in relevant part:

[A] person who knowingly has in his or her possession, custody, or control any obscene … writing … [or] any sticker, decal, emblem or other device attached to a motor vehicle containing obscene descriptions, photographs, or depictions … commits a misdemeanor of the second degree ….

But this covers mere home possession of obscenity, which is constitutionally protected under Stanley v. Georgia (1969); this entire provision is therefore unconstitutionally overbroad and thus invalid on its face, and thus can't be applied even to possession of obscenity in public.

Now maybe the charges will instead be changed to a violation of § 847.011(1), which covers "show[ing]" such obscene material. "Obscene" is defined in an earlier provision using the Supreme-Court-approved definition of obscenity:

(10) "Obscene" means the status of material which:

(a) The average person, applying contemporary community standards, would find, taken as a whole, appeals to the prurient interest;

(b) Depicts or describes, in a patently offensive way, sexual conduct as specifically defined herein; and

(c) Taken as a whole, lacks serious literary, artistic, political, or scientific value.

That statute, then, would be facially constitutional. But it couldn't constitutionally apply to Dillon's speech, because to be obscene, expression "must be, in some significant way, erotic," and must tend to arouse "lustful thoughts" or "sexual responses" and not just refer to sexual acts. Hard-core pornography might be obscene, especially if displayed in public; but this sort of vulgar verbal reference to a sexual act is far from hard-core pornography.

Dillon thus can't be prosecuted for possessing or displaying obscenity, and he also can't be prosecuted for resisting an officer, a charge that appears to be based solely on Dillon's refusal to redact the sticker.

The Georgia Supreme Court, by the way, struck down a ban on "profane or lewd" words on bumper stickers, see Cunningham v. State (Ga. 1991), in a case involving a man who was displaying a "Shit Happens" sticker; that's not quite the same issue as here, though.

Thanks to The Smoking Gun for the arrest report.