I help do archery demonstrations for some of my local faires. Generally as a safety measure, the faires my group participates in require non volunteer/cast to keep their bows unstrung at all times. We only string ours for demonstrations, tournaments, or gigs. And arrows are only set to string at the range, period. Carrying arrows as accessories is limited generally to target points. Best bet would be to contact the faire in question. Even if they don't have guidelines on their website or fliers about bows, somebody would be able to give you a definitive answer for that faire.
As an archer, even not as a participant, I would not recommend carrying your bow strung anyway. It looks better, and for some bows is what makes it obviously a bow, but any wooden or composite bow that would be period would actually suffer damage from being carried strung in the sun and heat for a prolonged period of time. It'll drastically increase string follow, where the boy stays bent permanently, and reduces or eliminates bow draw strength.
Also, on another personal note, please remember that bows are weapons. We did have somebody (not part of my group) at a local faire last year decide to do an impromptu bow demonstration, away from the range, without the faire's permission, and it nearly resulted in myself and two of my guildmates getting hit with an arrow.
