In British politics, rosettes (or sometimes flowers and ties) of a political party are often worn by candidates and their agents.
Electoral Commission guidance on rosettes
There are no rules in legislation specifically about rosettes but the Electoral Commission have developed guidance based on the inability to campaign in a polling station.
The guidance looks specifically at the wearing of rosettes by Tellers, but this is applicable to anyone.
Tellers may wear coloured rosettes or a badge of a reasonable size, as this assists electors by making it clear that they are activists and not electoral officials. The rosette/badge may display the name of a candidate and/or an emblem or description; the rosette/badge should not bear a slogan and must not be oversized.
Tellers must not wear, carry or display any headwear, footwear or other apparel that carries any writing, picture or sign relating to any candidate or party apart from a rosette.
Imprints
A rosette should have an imprint if it has a printed message or name on it, like for a poster. If it is just coloured material without any printed detail then an imprint would not be necessary.
Please see the link below and in particular paragraphs 1.18 and 1.19.
Guidance on the conduct of tellers in and around polling places (pdf).