Click on the user's name and you can reply to the VM on their profile. If you reply on your own, the other user will never know you replied. I wouldn't have known you replied if I didn't come back to your profile.
Can I make a suggestion? For you sig, can you make it a little smaller or change? You can get an infraction for it if it breaks the size rules. The size limit is shown here: Rules
(You have to scroll all the way down to the bottom of the post to see the signature rule.)