The person giving the tour knows security by obscurity is weak for actual security, but strong for marketing.
(Even random mentally ill people are likely to have access to firearms, and maybe heavy vehicles.)
Before cloud got big, I used to have a personal physical server colocated at a network facility, in a nondescript commercial building that you had to know was there, and turn off the main street to get to, with no signage I could see. (Also, biometrics scanners, when those weren't consumer things, and a waiting room that seemed to securely lock in visitors, in view of guards.)
I'd previously heard of non-government buildings without signage, for security reasons, so I figured that was it. Rather than not wanting to spend the money on a sign that would make it easier for customers to physically find, increase brand awareness, or raise their prominence in the minds of local officials before whom they might occasionally have business.
And, over time, you hear of other non-government unmarked buildings that are arguably "sensitive", for one reason or another. The ones that personally come to mind, historically that type has been threatened before (by, e.g., people angry at a company that they blame for automating away jobs, people who saw a movie involving blowing up records of bank loans and think that will work in real life, animal rights activists who want to free lab animals (and didn't see that other movie), eco-terrorists, people who are are mentally ill and found something conveniently located to fixate on). Maybe also no need to invite protestors?
Once went to visit a Raytheon technical support guy in his office. He made a point that it was 'hard to find' and there 'were no signs'. And he was right. Drive to a building. Park. List of business but not Raytheon. Go through a door that looks like it should be locked. Down a hall to the end. Open a door that looks like a utility closet and there is their office.
Company Policy.
Old office in SF two floors were a banking operation. They weren't on the signage. And you'd get in the elevator with people that worked on those floors and they would stand silently despite obviously knowing each other. Double set of doors on those two floors.
There's an interesting building right in downtown Minneapolis that takes up an entire block that I'd passed several times a week for years without even noticing it—it's the operations center for Wells Fargo (and actually it just recently has been sold).
Zero signage and very nondescript, but when I found out what it was some of the physical security around it started to become super obvious. Big bollard "planters" and protection from large vehicles, a lot of cameras, no real obvious lobby.
This is the building, it's fascinating to check out the street view all the way around the block: https://maps.app.goo.gl/UYKnA2Bs9gMQsSwo9
If I had to do it I’ll make it a boring unsuspecting commercial building with signage “storage R us” for example.
There was a time when I believed this. But over the years, I've concluded that in many cases, that which is considered legitimate security is in fact rooted simply in ensuring that the attacker is lacking information, which is fairly synonymous with obscurity.