Add this to a new Automator Actions item and save as a Service. Right-click or Control-click an app or kext to verify notarization. Optionally, run as a script in Terminal using the path to an app or kext as the first argument.

Verify App or KExt Notarization.bash

#!/bin/bash

testFile="$1"

if [[ "$testFile" != *'.app' ]] && [[ "$testFile" != *'.kext' ]] ; then
	theCommand='display dialog "This item does not appear to be an application or kernel extension." with title "Verify Notarization" buttons {"OK"} default button {"OK"}'
else
	testBinary=$( /usr/bin/stapler validate "$testFile" | /usr/bin/grep '64-bit' )
	
	# per the man page, stapler returns 0 on successful stapling or validation
	if [ "$?" != 0 ] && [[ "$testFile" = *'.kext' ]] ; then
		theCommand='display dialog "Warning! This kext is not notarized and will not be compatible with macOS Mojave 10.14.5 and later." with title "Verify Notarization" buttons {"OK"} default button {"OK"}'
	elif [ "$?" != 0 ] && [[ "$testFile" = *'.app' ]] ; then
		theCommand='display dialog "Alert! This applications is not notarized and will not be compatible with a future version of macOS Mojave after 10.14.5." with title "Verify Notarization" buttons {"OK"} default button {"OK"}'
	else
		theCommand='display dialog "Confirmed Notarization is valid."  with title "Verify Notarization" buttons {"OK"} default button {"OK"}'
	fi
fi

/usr/bin/osascript -e "$theCommand"