Database management systems have different definitions of acceptable characters for object names. Most names must begin with a letter and cannot contain spaces, backslashes, or reserved database management system keywords. Some databases allow special characters such as forward slashes (/), underscores (_), dollar signs ($), dashes (-), dots (.), or mixed cases. Sometimes the database allows you to use special characters or reserved keywords, or force mixed-case, uppercase, or lowercase names if you provide the object name enclosed in delimiters, such as double quotation marks.
However, ArcGIS does not delimit object names. Do not create any tables, feature classes, indexes, databases, users*, roles, or other object names that require delimiters if you will be using them with ArcGIS. The object will be created in the database, but you cannot access it from ArcGIS.
*Microsoft SQL Server user names containing special characters are delimited to fully support Active Directory Groups and Windows Authenticated logins; however, ArcGIS does not support user names containing single quotation marks or apostrophes.