If what you're worried about is being accused of backdating, then you could try timestamping your articles by some trusted third party. This way you can certify that a document/article was created before a certain date and wasn't modified further on (so in this situation that you've come up with some conclusion/investment decision in the real past). In case of a non-professional context some free services might give you enough credibility:
But backdating is only one of the problems you may encounter when trying to reliably report your performance. For example, timestamping won't help the fact that you can selectively publish only the trades that went well or just erase your prior poor record if it wasn't already disseminated. You could try to minimise this risk by keeping the window between actual transactions and publishing recommendations small (no "past trades" popping up in your blog out of nowhere), but in the end I suppose it's a question of trust - do your readers (clients?) feel they should/can trust you and foremost what's at stake (if you're only blogging personally it's different than if you're managing a mutual fund).
Reliable reporting is a much more complex topic, there are numerous examples of real problems occurring in professional context, thus guidelines like GIPS were created. But still, I feel there's no ultimate solution to the problem. Most of the time it's a mix of legal regulations, business reasoning (you can't really "cheat" your track record that much if you have to later pay it out), professional/ethical standards and some good faith. But sorry, that was probably too much of a digression.
Going back to your question, I think the most important factor is what your goal is. Are you blogging and keeping your transaction journal just for "fun" and educational purposes? Do you sell services/systems? Or maybe this blog is connected in some manner to a financial services company (managing client investments)? Presumably it's the former, but otherwise this would dramatically change the situation, and you would need to think about a much more complete and stringent solution to the problem.