add icon for sign pdf uno command

Change-Id: I918828a596a94e3b5aa02db22b93196fa2d8d797
Reviewed-on: https://gerrit.libreoffice.org/43289Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: andreas_kainz <kainz.a@gmail.com>

officecfg/registry/data/org/openoffice/Office/UI/GenericCommands.xcu

@@ -5924,6 +5924,9 @@
         <prop oor:name="Label" oor:type="xs:string">
           <value xml:lang="en-US">Sign Existing PDF...</value>
         </prop>
+        <prop oor:name="Properties" oor:type="xs:int">
+          <value>1</value>
+        </prop>
       </node>
       <node oor:name=".uno:MacroSignature" oor:op="replace">
         <prop oor:name="Label" oor:type="xs:string">