The Ramblas are very crowded, and mainly with tourists that look around everywhere and are relaxed. Burglars are really working all the day, 24 hour. We see them everyday close to the corners, sitting near the parked motocycles, waiting for the victims near one of the old Ramblas trees, etc....
Just put your bags close to your stomachs and if you are wearing rucksacks, put them on the front part of yourselves. Always control your bags and cameras. We always carry the bags where we can see them and we walk the Ramblas every day!
The Ramblas are also full of police wearing plain clothes and there are cameras everywhere so the place tries to be under control but burglars are really smart.
For men, some ladies come and touch just to detect where your wallets are. Keep alert!
Just keep these tips in mind and everything will be fine :-))
There's a police station in the Ramblas, nº 43. Just in case!