You cannot use the following characters anywhere in a site name, in a subsite name, or in a site or Active Directory group name:
tilde (~)
number sign (#)
percent (%)
ampersand (&)
asterisk (*)
braces ({ })
backslash (\)
colon (:)
angle brackets (< >)
question mark (?)
slash (/)
plus sign (+)
pipe ()
quotation mark (")
Site name cannot be start with an underscore (_) character or with the period character.
Folder names
You cannot use the following characters anywhere in a folder name or a server name:
tilde
number sign
percent
ampersand
asterisk
braces
backslash
colon
angle brackets
question mark
slash
pipe
quotation mark
You cannot use the period character consecutively in the middle/end of a folder name.
You cannot start a folder name with the period character.
File names
tilde
number sign
percent
ampersand
asterisk
braces
backslash
colon
angle brackets
question mark
slash
pipe
quotation mark
For ref click here
