I'd like to assume that if its YOUR house you can have whatever sign you want. But if you have a tenant and they are under the impression, based on this sign, that there is an active security alarm, that may be considered "false advertising" in a way or something of that nature... then again, if its not in your lease who knows... thats my two cents
BTW, a security alarm does not mean its connected to the police. My alarm for instance dials out to a central station who are under instructions to contact a certain list of people, NOT the police. You are not required to have it contact the police or any central station. However there may be laws in your area pertaining to having an audible alarm signal that does not connect to a central alarm company. So be careful of that... but an alarm that contacts a 3rd party, not illegal, however if that 3rd party contacts the police they may fine you without a permit if they were contacted by another party on the basis that a security alarm contacted them rather then an actual person making the call to police/central alarm, since its an electronic device.