the concept of "signing in" is not unique to a web page though, you also do it at a hotel. you also do it if you have dinner reservations. you also do it if you

the concept of "signing in" is not unique to a web page though, you also do it at a hotel. you also do it if you have dinner reservations. you also do it if you pick up a package at the post office. You also might do it when you show up for work to be put on the clock. sign in, check in, clock in, log in. its all referring to a social process that is unique to that engagement between those two parties. What is performed can be widely different, so it makes sense to go to these sort of common words.