I have a doubt about the phrasal verb "sign in."
Consider the sentence, "I signed in to a web site." Some write it as "sign into" and others as "sign in to". Because the phrasal verb is "sign in" only, is it correct to write "sign into"?
Actually, you sign in, in order to access all the features of a website; and you do the act of 'signing in' on/ or at a website that has been found via its URL but which then requires a password to access its features.
So, "I signed into a web site." would not make sense.
I signed in on the UsingEnglish website and...
I signed in at the UsingEnglish website and...
However, we sign in at a private members' club, at work etc - 'at' only.