When used in the headlines, symbols can in some cases lift the CTR, and in some others it can actually drop.
®: My experience has been great with this one. It helps to give the message of “we are the official site”.
?: Using question marks usually have a low performance, and yet many use them. I guess they don’t do A/B tests…
!: If we could use them, that would rule and I’m sure they would send CTR to the sky.
#: In some cases it can help. You should test it in order to really know.
Emojis: They are against AdWords ad writing policy so my suggestion is to not use them.
$: If you’re promoting a low price, it can help of course.
&: In all my tests it underperformed compared to “and”.
Know any other symbols that should be tested?
Here is some more info about the ad writing policy.