Anything you post on StackOverflow and its sister sites is automatically placed under a Creative Commons license. As such, all anyone needs to do to use the content is to follow the terms of that license. However, since the person requested to use your code in a production codebase that likely cannot be placed under a Creative Commons license (as is required by the license) then they will have to contact the owner of the content (in this case, you) to obtain a different license. Unfortunately, there is no mechanism built into StackOverflow for contacting another user (yet).
Alternatively, if you wish to dual-license (GPL, public domain, etc) your content here, you can put an appropriate note in your "About Me" section of your profile and people can choose the license under which they wish to use your content. Note that this will only apply to content you create - if you edit an answer, that answer cannot be relicensed without that owner's consent as well.