For people who don't understand dogwhistles, or need a good way to explain to someone what a dogwhistle is, use inside jokes as an example:
"I have a cat who, whenever I open up the door, he makes an absolute dash for it. I call him Leeroy Jenkins."
Now, most people's responses to the above might be, "Well, that's a weird name for a cat but alright." But people who are in the know, who get internet culture from a decade ago, will snort, because that one apparently entirely innocuous statement says these things:
- I am a netizen.
- I'm an early adopter. (old.)
- I likely played or at least am familiar with World of Warcraft.
And this means they can talk to me about other things. They know that if they say, "Leather belt!" I'll likely find it funny. And, crucially, my being in the community will make the community substantially more accessible to other old internet dorks who like classic MMORPGs. And you will never know, because shit like "Leeroy Jenkins" and "leather belt" and other inside jokes are innocuous at best, or, most likely, you probably don't even realize they're jokes. The only time you would is if someone points it out to you and explains it.
And this is where dogwhistles and inside jokes differ: People will explain inside jokes, but the whole point of a dogwhistle is that it doesn't get explained, and just remains under the radar. So you have people saying things in your community that you will never know are attracting a certain group of people — until someone tells you that's what's going on.
I'm certain you've seen how quickly little trends can take over a community: If I swooped in and became a very active member and started making World of Warcraft jokes, it would absolutely bring out other World of Warcraft fans — ones already in your server that you weren't aware of, as well as even some other new folks from outside — and before you know it (if you ever even do!), your community has become kind of a World of Warcraft community.
Imagine, now, instead of with World of Warcraft, this happens with fascism.
So generally, if someone tells you something is a dogwhistle, it's best to err on the side of caution to believe them. Ask them to explain it, but don't discount it; act on it.
*(also I never actually liked World of Warcraft)