Realistically, the code and details of are covered by NDA. The task solved, the huge difficulty of same, the overall success of the task being solved, demonstrable fluency in related but public areas of computer science, and the commercial success (modest or otherwise) of the code would not be.
If you don't understand this, or couldn't say the same things about what you're doing, maybe you're not working at the same level, and you are welcome to go fire up the GitHub account and solve tic-tac-toe in Haskell or whatever the hell it is that's meant to be so impressive.
The closest analogy I can come is - say you wrote a pile of LEDA (not a invite to debate if this is a good product, but it's certainly substantial) and you've got references who are in a position to know that say, 'yes, Joe Bloggs really did write all the graph algorithms or geometry algorithms or whatnot in this package'.
Well, you're within your rights to 'not believe a word you've said'. But this falls into the thing I'm complaining about - the whole pathological distrust of programmer achievements. How do you think engineers or commercial research scientists in other fields ever get hired, for fuck's sake?
There's a distrust of programmers because many programmers are not at your skill level. You don't seem to have problems with finding employment. Perhaps open-source contributions don't matter to people of your caliber. But you need to realize that it's not HR or management asking to see your code -- it's your peers.
We need as many metrics as we can to find out who's good and who says they're good. Looking at code and examples of work is exactly how you do that. You can argue all you want, and it may not be fair. Neither is "You have to have a 3.5 GPA to get a job here."