Spotted a cobalt blue & a lilac (pink) Brompton locked up to bike stands in Edinburgh very late at night - seemed to be left there for the night, with bikes in unfolded state. Highly unwise, especially if done on a regular basis.
On very rare occasions that I've had to lock up the bike I fold it and pass the lock through the full folded package and round the locking point, making it very hard to cut the lock.
Really do need to make folk aware of how vulnerable Bromptons are when parked like this.