I don’t normally deal with UX design, but during the design of a new web app I was developing for a client, I ended up pondering which form of language I should be using for logging in to the app. Some companies/projects like use “Log In” others use “Sign In”, and then on the flip side “Log Out” or “Sign Out”. Which of these are the correct terminology to be using and why? Luckily I’m not the first person to ask this question, nor the first to seek answers.
In the course of my investigation I found that it really takes back to when we learned about grammar in school (English grammar that is). It really ends up depending on WHAT you are trying to get across to the user, and whether or not they will be performing an action.
This is where grammar comes into play and gives us the focus on the difference between the object (noun/adjective) and action (verb)  .
- “login” is actually a noun;
- i.e. – “Where is the login page?” or “Here’s the login”
- In contrast however you are going to “log in” to the web app
Should I be using the “Sign” or “Log” form
As for using “Sign” vs “Log” terminology, it was noted that in the study published in “Homepage Usability”, by Jakob Nielsen, that a number of large sites are using the “Sign” form as compared to the “Log” form . Within this same thread on Stack Overflow, another user provided a different study by another author that had the same conclusion in terms of it’s survey .
Which one is right for you though?
This depends on what you are trying to convey to the users of your site:
- Use “Log” if you want to promote a technical or formal tone;
- i.e. — accessing a “secure” terminal
- Use “Sign” if you want to promote a casual tone;
- i.e. — signing the sheet of paper indicating when you have come and gone
As an aside, this also applies to “Sign Up”, “Create an Account”, or “Register” as well. It depends on what tone you want to set for the user.
Personally, I prefer to use the “Log” form for my apps, but only because I am technical. I could just as easily go with “Sign” if the client desires to tone the app casually. I also prefer “Register” over “Sign Up” for the simple reason that it isn’t too close to the “sign” or “log” forms.
The one thing that I haven’t mentioned, is to maintain consistency. I can’t stress this enough, nothing irritates users, and developers alike than having conflicting terminology through out your application.
 : http://www.grammarly.com/answers/questions/4300-logout-and-log-off/#answer_5333
 : http://ell.stackexchange.com/questions/1362/difference-between-logoff-logout-signoff-and-signout
 : http://ux.stackexchange.com/a/1084
 : https://web.archive.org/web/20130416031325/http://0xtc.com/2009/06/25/login-logout-vs-sign-in-sign-out-vs-log-in-sign-out-a-short-roundup.xhtml/
 : http://ux.stackexchange.com/questions/1080/using-sign-in-vs-using-log-in/1085#1085