
This is on a shirt I got for free once and now it's driving me crazy!
I strongly suspect it isn't a rebus at all, but a geeky joke about (workplace?) informality.
In some text editors and Unix text-processing tools, the notation s/thing1/thing2/g means "replace thing1 with thing2 everywhere". (I think s is for "substitute" and the "g" for "global".)
So it's saying "replace ties with trainers[1]", which might mean something like "get out of work and go running" or "wear informal clothes to work rather than suit and tie" or "get out of work and sit around at home in comfortable gear". (My guess is that it's the second of those, and that the shirt is actually advertising a company to prospective employees, suggesting "if you work here you won't have to wear a tie". Is there anything on the shirt that would give a clue?)
The target audience is probably either programmers or Unix system administrators.
[1] Sports shoes. Pumps. Whatever the local term for them is. Where I am, it's "trainers".
As Gareth explained s/thing1/thing2/g means global substitution of thing1 with thing2 in the programming world.
So, here it could also mean
Work is fun or stretching it further ( as I am a programmer :P), programming is a work where work is substituted with fun.
s/thing1/thing2/g is not a regex. It's a command in ex (and, by extension, vim) and sed. thing1 is a regex within this command.
– wchargin
Jan 27 '17 at 17:59
I was reading it as
"Sing".
Because
1. the tie looks like small-letter "i" ; with a round head.
2. the black stripe of 2 shoes together forms an "N" of capital letter
gdoes mean "global". The thing between the first two slashes is a regex, and after the last one are its flags. The flags might also define how many times things are replaced per line or per file, or how the overall program behaves, depending on the program interpreting it. – Jan 27 '17 at 15:19