Although we don't have a built in feature to do this, it is possible with a little custom CSS:
Try adding this in the Custom CSS in the settings of your OptimizePress 3 page:
a[target="_blank"]::after {
content: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAQElEQVR42qXKwQkAIAxDUUdxtO6/RBQkQZvSi8I/pL4BoGw/XPkh4XigPmsUgh0626AjRsgxHTkUThsG2T/sIlzdTsp52kSS1wAAAABJRU5ErkJggg==);
margin: 0px 3px 0px 5px;
}The result is a little like this:

For example:
a[target="_blank"]::after {
content: url(https://www.yourdomain.com/yourimageurl.png);
margin: 0px 3px 0px 5px;
}Hopefully this tip is helpful in you styling your links a little more !