I have been using two cheap thin cable locks to encircle (vertical) both sets of panniers. This keeps the panniers closed and locked to the racks and one or both of the cable locks go through a bike rack or around a post.

Both cables are easy to cut if someone really wanted to steal the bike. I consider them more of a nuisance locking measure than a serious security solution. They will stop casual theft but not someone determined/professional from stealing my bike. My next big tour is up the Rhine river, down the Danube river and a train to Prague to ride down the Elbe river next summer. I am considering a heavy duty chain lock for that trip as I will spend a great deal more time off the bike.

As to making my bike look less valuable to prevent theft, great idea but I think having a full touring rig outfit kind of defeats the attempt. Nothing screams "expensive" more than matching Ortlieb front back and handlebar panniers. Having said that; I did buy a 2015 Specialized AWOL Comp in flat black with black lettering on black...well you get the idea. It certainly does not yell "HEY LOOK AT ME!!!"