It seems that Foxit merged Ink Signing and their eSign service. I can understand why eSign would not be available in the PA, as it requires a local service to run. But without the UI for it, it doesn't seem possible to switch to Ink Sign.
The full app appears to use the following Reg entry to control which version of signing is active:
[HKEY_CURRENT_USER\Software\Foxit Software\Foxit PDF Reader 11.0\plugins\FoxitSign]
I tried creating that key in the portable app, but the ribbon bar still doesn't show up. Neither does the PDF Sign entry in Preferences, where the eSign service can be permanently disabled.
Is it possible to get Ink Signing back in the portable version?