For this, and other use-cases, special casing Numpy arrays stored in object arrays does make sense:

"If this is s a Numpy array, pass the operation through."

Because we now (development) use rich compare, the result looks like

Oops, not what was intended. In fact it raises an error

In [7]: b
Out[7]: array([array([ 1.,  1.,  1.]), array([-1., -1., -1.])], dtype=object)

In [8]: sign(b)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-8-3b1a81271d2e> in <module>()
----> 1 sign(b)

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()