No alarm system is going to stop "savvy burglars", but that's only half the story.
Point 1 - WiFi Isn't Your Biggest Problem
If you have ANY alarm system decal, the answer is always "if I cut the phone/cable lines, there won't be a notification sent to the police/alarm company" (and those utilities are generally available outside the house). Why cut just the WiFi when you can shut down the whole house? Heck, I can take out the whole block at once if I just do a basic scan for the community box.
It makes an argument for a cellular connection that you can use as a backup, but that's a price/reward thing.
I know you're now thinking "then it'll be brilliant of me to have an alarm system with no decal!" - see Point 2.
Point 2 - You vs. Your Neighbor
A savvy burglar is one who takes the path of least resistance. You and your neighbor both live in the same area and probably have around the same income, yet you have an alarm system (which you have advertised having) and your neighbor doesn't. Which house is a "savvy burglar" going to aim for?
This is the main point of home alarm decals. Even without an actual alarm system, they reduce the occurrence of burglary.
(the same goes for dogs, BTW)
Point 3 - It's Only So Good Anyway
Alarm systems are just a better version of locks - and we all know that the purpose of locks is to keep the good guys out.
Starting with this fact: if you're a truly high-value target, someone who wants in is just going to ring your doorbell in broad daylight and have you let them in - then go about their thing. The alarm system becomes moot.
But we're talking about "savvy burglars" who approach in the night. In that case, first see Point 1, because that's happening with or without a sign in your yard (you might not have bothered to put up the decal, you could have smart home stuff, you might not have a cell phone handy for dialing 911... there are reasons). But past that, if they're savvy they're going to run a good magnet detector along your doors/windows, and if they find one they're just going to set up a strong magnet to defeat the reed switch in your door/window. Or, more likely, move on to your neighbor (Point 2) - because you might have infrared motion detectors, and those are still defeatable... but are more annoying.
No matter how you slice it, short of exotic scenarios where you are concerned about personal assassination or burglary of something very specific that only you own, advertising an alarm system doesn't hurt you. And I do mean exotic versions of both things, not that those scenarios are exotic (though they are).