http://www.police.gov.hk/info/doc/pgo/en/Epgo006.pdf
34. A police officer shall at all times abstain from any activity which is likely to interfere with the impartial discharge of his/her duties, or which is likely to give rise to the impression amongst members of the public that it may so interfere. In particular, a police officer shall not participate in political activities as defined at the head of this Chapter, except:
(a) to cast his/her vote as a registered voter; or
(b) when on final leave AND permission has been obtained from the
Secretary for the Civil Service to participate in election or electioneering
activities in relation to HKSAR Deputies to the National People’s
Congress (NPC) and/or Election Conference for the NPC Elections; or
(c) permission has been obtained from the Secretary for the Civil Service to
participate in Village Representative Elections in accordance with CSB
Circular No. 9/2010.
'Political Activities' include, for example:-
(a) lending support to, or participation in political activities of a political
organization;
(b) speaking publicly, including to the media, on matters of a political
nature other than in the course of official duties;
(c) distributing political publications;
(d) promoting or advocating political views or the electioneering platform
of any candidate; and
(e) canvassing or campaigning on behalf of a political organization.