I'm finding this incredibly frustrating and am in a minority of one so it feels quite isolating.
Firstly, anti-racists don't have a problem with blackboard, whiteboard, black coffee, white coffee, anything else that's descriptive. It's just descriptive. That said, I went into Starbucks on Friday, asked for a white tea and got something really odd. Apparently, there's some actual tea called 'white tea' that isn't builders tea. I've got no idea what it is, but it wasn't what I wanted. Under these circumstances, it would have been better for me to ask for tea with cow's milk. Point being, sometimes the descriptors fall down because what one person's describing isn't what another person's hearing as being described.
Secondly, these problems that supposedly we (anti racists) have are largely invented by people who want to have a go at the 'PC Brigade'. They just don't really exist and are, instead, set up as some kind of 'straw man' - i.e. for arguments sake so that you can pull them apart, burn them down, destroy them really easily. Once you do that, you can expose how 'silly' ALL the anti racist arguments are ...
Thirdly, I've actually now run this past some of my friends who are black with the question 'Do you think this sign should be changed and, if so, why?' Basically, they said that the sign itself isn't a problem, but it doesn't exist in isolation. The words can be taken out of context to mean something else. They can be used as justification for something much more damaging. The example one person gave me was the confederate flag in America. By itself it's just a flag, but in the wrong hands it can be weaponised and become a symbol of something far more sinister - like the American far right are doing now, killing people, in the name of that thing that was 'just a flag'.
^^ Now that seems a million miles away, doesn't it, but I actually have a dog in this fight. My family are Jewish. Over the years we've been subjected to graffiti on our cars, stuff shoved through our letter boxes and random verbal attacks in the street - walking to synagogue with the men wearing 'skull caps' kinda makes you stand out. We have, if you like, an 'ancestral trauma' relating to the Holocaust. It makes us twitchy. When someone tries to wipe out your entire 'race' from Europe and obliterate your history (repeatedly), you tend to be a little bit on your guard. You end up knowing how small things that people say and do can lead to mass murder 15 years down the line. Now, I'm not saying this is what's happening here, but I _am_ saying it's easier to get triggered, especially when you're in a minority of one, and when all we're actually asking for is some sensitivity, some understanding of where we might be coming from, and less 'baiting' so we don't have to constantly justify why we're scared, in reality, really very scared.