A graphic artist I know contributed (pro-bono) this draft, unofficial, composite SAML logo idea. The files are stored in the SSTC document repository, and are essentially the same image(s) in various file formats..
The .psd format file is the Photoshop source file.
Note that this logo image is composite -- all the various comonents are separable, eg the abstract glyph can be used anywhere in relation to the "SAML" text, or not at al, or on it's own. The version text, eg "v2.0", can be present or absent.
This is unofficial and only a draft. The SSTC may need to decide if it wishes to adopt a "logo" for SAML in an official sense.
[updated 20-Oct-2008: added links to draft unofficial logo files, cleaned up text.]