Guild Wars 2

do sigils on your off hand effect your main hand skills?

Yes.

It doesn’t matter what hand (or armor slot) any of the upgrades are in. If you are wearing it (or holding it) you get the benefits of it.

so if my main hands has a bleed, could i put the bleed duration sigil on my off hand and it still work on my main hand?

Here is a great post on how sigils work.
Note that you can go into the Mists and test sigils there before purchasing.

http://www.reddit.com/r/Guildwars2/comments/10ilke/how_sigils_work/

I;m not sure about this..If i wield for instance sword main hand + mace in off , have sigil of quickness on sword and something entirely different on offhand,its getting obvious for me that quickness activates much more , since autoattack only uses mainhand weap,and my other sigil really only gets activated if i start using skill 4 – 5.

They certainly should, if they don’t, since we dual wielders have to pay double the price for our weapons that 2H wielders do.