The best replacement for sign in is log in.

The best alternatives to sign in are rated as following:
★★★★★  log in
★★★★★  sign on
★★★★  create an account
★★★  sign up
★★★  sign-in
★★  login
★  sign in

Your alternative for sign in is not listed? Suggest!
Speaking about sign in, one probably shouldn't forget about yahoo.

Other search terms related to sign in and their ratings are:
★★★★★ yahoo
★★★ messenger
your windows live id
You have in mind a companion for sign in and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of sign in in all years. Click on graph for more.
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