WiseStamp can be added to Gmail 2 different ways: via the Google API or through the WiseStamp extension for Chrome.
If you're seeing 2 signatures at the bottom of your email you probably have both signature types enabled.
Follow this link to open your permissions setting and remove WiseStamp.
Click on the WiseStamp option to reveal the blue REMOVE ACCESS button.
Remove the access, and refresh your Gmail. You should then only see 1 signature in your emails - being added from the Chrome extension.
If you are still seeing 2 signature, make sure when you opened the permissions link it is opened with the email address where the signature is showing.
You can check this on the top right of the link, as shown below.