The short answer is yes.
Whilst it would be hard to go into exactly how here, there are a couple of things to note. Firstly, KeyPOST doesn't consider how the sign is to be attached to the support, it assumes that a suitable fixing is available. Secondly, there are two ways that people consider what a cantilevered attachment is, either using clips into the channel behind the sign, with a small portion of the sign overlapping the post, or a 'true' cantilever where no part of the sign overlaps the support. Of course, in the latter case and if this for example was a triangular warning sign, some sort of channel or other horizontal attachment from the top part of the sign would be needed. KeyPOST doesn't need this as it assumes some sort of fixing will be in place. You can of course add channel to the sign if you want to see this. Have a look at the two images attached as files to this post. IN the one showing a triangular sign I haven't added any channel so it seems impossible but KeyPOST can still verify the design is a valid structural overall.
If you want more information about exactly how to achieve this please feel free to give us a call and we can try to set-up a screenshare to talk you through the process.