Well, he should have given you the yard sign when he was there. Personally, I don't want a yard sign, in case a criminal is familiar with different types of systems, how long it takes to go off, how long it takes them to alert police, etc. So, I wouldn't care that much if there were no sign. There also is sometimes a charge for the signs.
When I ordered my service, I also signed a contract after it was installed. If I had suddenly refused, it would've been easy enough for them to uninstall it or to refuse to activate it. Why did you sign what was clearly a contract without at least scanning it and asking the guy for a summary of what it was saying? You signed the contract and had opportunity to look it over had you chosen to do so. Unless you were mentally incapacitated, you're probably stuck in the contract for the next 3 years unless there is an early termination opion.
$30.26 per month sounds like a great deal for security monitoring. Mine is a lot more than that. Also, be sure to ask your homeowners insurance company about their discount for maintaining a monitored security system. They will need a copy of the contract as proof of the monitored service, and the discount should be about 10-20% of your annual premium.
Finally, if you really want to talk to them and are being ignored, then intentionally set your system off long enough that it will notify the service (30-45 seconds?). The service will call you about the alarm, and then you'll have them on the phone! THe other option is to not pay them next month, and you'll have them on the phone at that point, too.