These labels are not necessary unless you intend to use the ``:ref:`` directive to point to them.  So you can feel free to remove them unless you add in some ``:ref:``s.  

Also, these labels are shared globally across all of the astropy documentation.  So I recommend using a slightly more descriptive name to avoid collisions with other subpackages.  Something like ``.. _models_design``.  

This comment applies to all the other .rst files with labels, as well.