vermummt - hooded, mummed (adj.), in disguise
die Vermummung- mummery
vermummen - 1: (vt) to wrap up (warm) ... 2: (vr) ... b: (= sich verkleiden) to disguise oneself ...
tief vermummt - heavily disguised;
vermummte Demonstranten - masked demonstrators
Vermummung - disguise; (von Demonstranten) covering of the face
Vermummungsverbot - das Vermummungsverbot by Demonstrationen - the law requiring demonstrators to leave their faces uncovered
vermummen - a: (einhüllen) wrap up [warmly]; b: (verbergen) disguise;
vermummte Jugendliche - masked youths
Vermummung - a: zur Vermummung hatten wir ... - in order to disguise ourselves we had ...;
Vermummung soll unter Strafe gestellt werden - wearing a mask is to be made a punishable offense;
b: (Kleidung) disguise
Vermummungsverbot - ban on wearing masks [during demonstrations]
it showed the extent to which the leader of Mexico's so-called Zapatista guerrillas, masked subcomandante Marcos, has become a symbol
Zapatista Guerrillas Set for Nationwide Tour ... As in a 2001 trip to Mexico City, the masked guerrillas will travel without weapons and with authorisation from the government
More than a dozen of their masked and armed guerrillas, including at least four women, remained in full control of the compound
Masked Palestinian demonstrators use sling-shots to hurl stones at Israeli border police
one small group of demonstrators, masked and black-clad, ran through the streets smashing windows and spraying paint
some Winnipeg police officers seemed to be more concerned about the masked demonstrators on their streets.
Masked demonstrators gathered outside the Church of Scientology in protest against the organisation
Masked protesters cause scene at I-69 office ... Window broken out of office door during protest against extension of I-69 through area ...
The Quebec police force admits that three masked protesters at the Montebello summit were undercover officers -- the same men accused of trying to incite ...
Hunt kennels staff attacked by 40 masked protesters
A masked gunman opened fire in this central French city on Monday, killing four people
A masked gunman stands in the northern Lebanese city of Tripoli
A masked gunman forced his way into a Chatsworth-area home early Wednesday, ... The assailant, a heavyset man in his 20s with a bandana over his face
Masked gunman robs 7-Eleven store ... He was wearing a red bandanna over his face
Masked gunman robs at least 8 businesses. ... He always covers his face, sometimes using a bandanna or ski mask. ...
DETECTIVES are searching for a masked gunman who tied up terrified staff ... Carrying what appeared to be a shotgun, the balaclava-clad man ...
Masked gunman robs shop's takings ... "He was wearing a dark coloured balaclava"
The assailants, who looked like masked police commandos, beat the entire family up
Four Palestinian shepherds were assaulted Sunday evening by masked assailants near the West Bank settlement of Susya
Black-clad, masked assailants torched a German cultural center Friday in Togo's latest post-election violence
I agree that this meaning still seems to be missing, so I would support finishing the correction, however belatedly. A paraphrase such as 'with one's face covered' would of course also work in some contexts, but a couple of entries with something like 'mask(ed)' would probably be clearer in the dictionary.
The major bilingual dictionaries only give an explanation for Vermummungsverbot; that also seems reasonable to me. It would be helpful to add to LEO, because it's not a law non-natives are necessarily familiar with.