Looking recently at references to code entries, I see most are in the format:

author, year, in Astrophysics Source Code Library, record ascl ID

For example: Barnes, J. E., 2011, Astrophysics Source Code Library, record ascl:1102.027

Using the entire ascl ID (ascl:xxxx.xxx) in the reference enables ADS to more easily pick up the citation. It may be helpful to the reader to include the name of the code as well:

Barnes, J. E., 2011, ZENO, Astrophysics Source Code Library, record ascl:1102.027

The ascl ID number can be used to provide a link to a particular entry. For the example above, typing ascl.net/1102.027 into your browser brings up the entry for the code ZENO.