What you are looking for is the Claims Username Format
<IdentityClaim>:0<ClaimType><ClaimValueType><AuthMode>|<OriginalIssuer (optional)>|<ClaimValue>
Where:
<IdentityClaim> indicates the type of claim and is the following:
“i” for an identity claim
“c” for any other claim
<ClaimType> indicates the format for the claim value and is the following:
“#” for a user logon name
“.” for an anonymous user
“5” for an email address
“!” for an identity provider
“+” for a Group security identifier (SID)
“-“ for a role
“%” for a farm ID
“?” for a name identifier
"\" for a private personal identifier (PPID)
"e" for a user principal name (UPN)
<ClaimValueType> indicates the type of formatting for the claim value and is the following:
“.” for a string
“+” for an RFC 822-formatted name
<AuthMode> indicates the type of authentication used to obtain the identity claim and is the following:
“w” for Windows claims (no original issuer)
“s” for the local SharePoint security token service (STS) (no original issuer)
“t” for a trusted issuer
“m” for a membership issuer
“r” for a role provider issuer
“f” for forms-based authentication
“c” for a claim provider
<OriginalIssuer> indicates the original issuer of the claim.
<ClaimValueType> indicates the value of the claim in the <ClaimType> format.
http://social.technet.microsoft.com/wiki/contents/articles/13921.sharepoint-2013-claims-encoding-also-valuable-for-sharepoint-2010.aspx