I have the same issue as "adam_1234 10-Aug-2016 08:57 "
There is a long wait for the signature to appear when clicking "sign", in Fill & Sign mode.
It is a saved signature image - I can only suspect that there is a problem with the signature image itself meeting ideal criteria...?
We apologize for the delay in response to your query.
If you are still experiencing the same issue, then you may try installing the latest update of Acrobat Std DC and see if that makes any difference.
Also, as you have mentioned above that it happens only when you add a signature image. Then please ensure that the size of the image should be so large.
Let us know if the issue is still unresolved.