On 25/02/2016, a request was sent to IANA to register Sirtfi as an assurance profile, on the guidance of Leif Johansson. Once completed (if successful!) Sirtfi will be listed here https://www.iana.org/assignments/loa-profiles/loa-profiles.xhtml
IANA Registration: http://www.iana.org/cgi-bin/assignments.pl
Assurance Registration Description: http://levelofassurance.org/process.html
OASIS provides detailed documentation of asserting compliance with assurance profiles: https://wiki.oasis-open.org/security/SAML2IDAssuranceProfile
Sirtfi Compliance Extension
<EntityDescriptor ...>
<Extensions>
<attr:EntityAttributes>
<saml:Attribute NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri" Name="urn:oasis:names:tc:SAML:attribute:assurance-certification">
<saml:AttributeValue>https://refeds.org/sirtfi</saml:AttributeValue>
</saml:Attribute>
</attr:EntityAttributes>
...
</Extensions>
...
</EntityDescriptor>