You can mark a category as being reserved for disabled people.
On your seating plan, a wheelchair icon will be shown on each seat that belongs to such a category. 

Mobility seatings are not a per-seat setting, it is its own category. That way, you keep full control to display wheelchair icons on the seats, or give them a different colour and pricing if you wish to do so. 

Pretty simple. From within the module, determine for each category whether or not it’s an accessibility category, and click the wheelchair icon to make it light up.

Then, assign the proper categories to your seats. 

After being saved, your seating plan  will show a wheelchair icon on the seats (and sections!) that have been assigned this category.