valid_name

Returns 0 if the specified string is not a valid identifier or a number other than 0 if the string is a valid identifier.

valid_name(character_expression)

character_expression: is a character-type column name, variable, or constant expression of char, varchar, nchar or nvarchar type. Constant expressions must be enclosed in quotation marks.

Creates a procedure to verify that identifiers are valid:

create procedure chkname
@name varchar(30)
as
     if valid_name(@name) = 0
     print "name not valid"

valid_name, a system function, returns 0 if the character_ expression is not a valid identifier (illegal characters, more than 30 bytes long, or a reserved word), or a number other than 0 if it is a valid identifier.
Adaptive Server identifiers can be a maximum of 30 bytes in length, whether single-byte or multibyte characters are used. The first character of an identifier must be either an alphabetic character, as defined in the current character set, or the underscore (_ ) character. Temporary table names, which begin with the pound sign (#), and local variable names, which begin with the at sign (@), are exceptions to this rule. valid_name returns 0 for identifiers that begin with the pound sign (#) and the at sign (@).
For general information about system functions, see “System functions”.

SQL92 – Compliance level: Transact-SQL extension.

Any user can execute valid_name.