From Eric Smith:
"Police appeal after teenage girls kissed and touched in alleged bus incident", Isle of Wight County Press, 3/24/2016.
In today's enlightened society, why shouldn't teenage girls kiss and touch?
I think this illustrates that, in a British headline
* if a verb form is ambiguous as between a preterite tense and a past participle, the past participle is probably what is meant;
* if the syntax is ambiguous as between a standard sentence and an abbreviated sentence, the abbreviated sentence is probably what is meant.
As a secondary point, I suspect that "appeal" is intended as a noun, so that "Police appeal" is a nominal and not a clause.