It depends on whether I am Riding the Dutch or the Trek Bike. Also it depends on what Socks I am wearing or if I have Bike Clips. With Dutchy I have a Chain Guard,with Trek I dont and I usually can Stuff my Trousers Bottoms in my Socks or if I have Bicycle Clips I Clip the Trousers Legs with them .On the other hand if I have no Clips and my Socks are loose and I am Riding Trek then I have to turn up my right Trousers Leg, Decisions Decisions.It is an International thing turning your Right Trouser Leg up,not just for the Americans.Dont forget to Rub the Gear Grease into your Leg to stop your Ankle from Freezing,I am Joking.
That's seriously one of the reasons I prefer always to wear skirts and dresses. The pictured riders are rocking the look, but I can't pull it off. If I wear trousers, I prefer the always chic ankle strap :)
A lot of our Cycle Bods do not bother to Roll up their Trouser Leg and just take the chance their Trousers are not Ruined,they dont like the Cold hitting them on their Leg. It Helps if you are Young enough to Wear Skinny Legged Jeans ,so the Chain does not Rub of the Leg,but as I said a lot do not worry either way about it.They are not as Tidy as the Americans.
I do the trousers-in-the-sock thing too - very uncool but it's too cold and wet to be exposing any skin just yet! Most of my trouser cuffs bear the scars from where I forgot or thought I'd take a risk... Oh and wellies make great cycle clips when it's cold and wet
I don't like trouser clips because they make my pant leg too tight against my knee and I hate that feeling. Of course, if someone would just make a chain guard for a front derailleur we would all be fine (and yes, they can be made. I have one, on a triple, and it works perfectly.)