One sock reads “One foot here”, the second reads “The other is there”. This idiom «одна нога здесь, другая там» (odna noga zdes’, drugaya tam/ one foot here, the other is there) means (of a person) someone goes or runs somewhere and returns in a very short time, very quickly (often used as a command).
It’s just a joke about being stuck with the bridges in st. Petersburg city. There are bridges across the city that are raised to let the ships through. And it leaves people unable to cross the river for quite some time. That’s why you can see the bridge on the socks.
You can buy the socks on myfriday.ru