If you use watson.search(), then the results are by default ordered by relevance. If you set ranking=False, then the result ordering is whatever is fastest for the database. Not very useful.
If you want to order by a field on a model, then use watson.filter(), which gives you a queryset of a single model, allowing you to use .order_by() to sort by a field. This only works when searching one particular model, and cannot do multi-model searches.
Ordering by a model-specific field using watson. search() is not supported.