In the street outside, runners were stretching and signing in for the five K race, which would begin shortly.
And signing in ASL is not very effective as there is no one-to-one correspondence between signed and written phrase.
Police could look at known troublemakers signing in at their local police station during the Leeds v Hull game.
If you use your phone for banking or other uses involving money or password entry, then a hacker could retrieve your IDs and passwords, especially if you use the "Remember Me" option when signing in.
You earn 60 additional points for signing in each day, which motivates people to continue to use the site.