Conditional if is single and part of the custom taxonomy

The first problem is that you’ve got a space in the first argument of has_term(). If you want to check for any term then you need to pass an empty string, but a space is not an empty string. Then, as documented, the second argument needs to be the taxonomy name.

This should work:

if ( is_single() && has_term( '', 'us_pf_category' ) )