Yes, ShipStation can automatically sign your customs forms!
Head to your Account Settings (the gear icon in the upper right).
Next, select Shipping and then International Settings from the sidebar on the left.
Here you can set defaults for customs information, and fill in the Sign Customs As field.
Generally, you want this to be your actual name versus your company's name.
Please note that FedEx is only able to sign customs forms with the Return Address Name listed in the Ship From Location selected for the order. For more information on editing your Ship From Locations, check out this article.