The ticket you were issued for blocking the sidewalk may very well be valid. The officer may have signed the copy of the traffic ticket that he kept. Your copy may not reflect (or legibly show) his signature.
Even if he forgot to sign the ticket, he could still testify to his observations. So, while you may wish to fight the ticket on technical grounds, don't be surprised if the court (or the prosecuting attorney) doesn't let you off the hook on these technicalities.
While I don't practice in your state, here is my take on your question.
Generally, something like small details will not render the ticket unenforceable, however, in light of the fact that he/she failed to sign it, you may have a good defense, since he/she failed to swear to the ticket, which requires a signature. HIre a lawyer and fight it.
I'm guessing your traffic ticket in Michigan was computer generated in the officer's car. It is not uncommon for that type of ticket not to be signed and it does not invalidate the ticket. Blockading does not have any point and does not go on your record.
It doesn't hurt to set the case for a hearing in traffic court and explain the situation to the court. Make sure first by speaking to the court clerk to see if the court has a practice of imposing costs for having a hearing, however. If the court is going to impose costs for the parking ticket, you should probably just pay the ticket.
The statute requires that tickets be signed...but blocking a driveway is a non-moving violation that has no points and only a small fine. Unless you are very wealthy, i can't see spending hundreds of dollars fighting a principle to avoid a $100 ticket.