Just a point of logic wouldn't you be alarmed if there was less of a police presence after a terrorist attack?
Good point.
I tend to be a bit of a realist, or alarmist, depending on your point of view.
If there is a normal police presence after a terrorist attack (which is what I assume you meant), then chances are it was an isolated nutjob. They check stuff out, they swarm, they gather information, they leave when they are done and the streets go back to normal. That is a how police run a typical investigation.
If there is a massively increased police presence on the streets after a terrorist attack, to the point where a local politician tells me "do not be alarmed", then I just assume politicians are doing what they always do: Lie.
Basically, they know there are more organized terrorists out there, so they are mobilizing all resources to get them (as they should). Maybe they are telling the truth, but I believe only a simpleton would assume this. It costs nothing to be alarmed and alert, but the rewards are enormous.
When seconds count, even the best police are minutes away.
I guess it could be summed up as this:
Whenever there is an massively increased police presence on the streets, as a rule, citizens should be alarmed and on watch... that is, if they value their lives or freedom.