Twice a week I visit a therapist in north London. It’s a couple of bus journeys from where I live, and these trips are normally uneventful. But one day, in early November, I noticed graffiti on my stop: “IUDE RAUS!!!” with a Star of David underneath, a red line through it.

I was paralysed by a combination of shock, revulsion and confusion. I don’t speak German but even I know that Iude isn’t Jude. I briefly – idiotically – thought it could be a pro-Jewish slogan that had had the Star of David crossed out by a different hand (that line alone was red). So I went home, troubled, thinking.

Two weeks later, the graffiti was still there. I took another picture – by this time someone had inexplicably added their Instagram handle to it, but there didn’t seem to be a connection. Clearly, “Iude” should have read “Juden” and “raus” was “out” – this was the work of an illiterate antisemite trying to say “Juden raus” – “Jews out” – in German.

So what to do? I rang the council, but none of its menu choices seemed to address complaints about graffiti or racist sloganeering. I left a message with a service that seemed the best fit.

The next Tuesday, it was still there. I was furious – but not talking to anyone else about it. It was just worming round in my head, like a parasite.

On the Thursday I bought a can of black spray paint, and on Friday I obliterated the words with a big black square. I hadn’t done anything like that since the 1980s when, having taken my boyfriend home to Cumbria, I spent 10 minutes in a mix of fury and shame scraping a National Front sticker off the door of an Indian restaurant where we had been planning to have dinner.

I took a picture of my black square. Then I felt guilty. My black square was pretty ugly. I’d defaced a bus stop. I wasn’t worried about anyone catching me: I had a good reason, if challenged. But all kinds of feelings rushed in on me. It was only then that I told my therapist, who is Jewish, the whole story.

Two weeks later, I checked the stop again. Someone had scraped a giant SS and a swastika into the black paint

I’m not Jewish, but my life weaves in and out of Jewishness and Jewish people in a way that’s wholly positive. I light a yahrzeit candle every year, on the anniversary of my younger sister’s death. I took my daughter to Amsterdam because she had read Anne Frank’s diary and wanted to visit her house. Freud and Proust are like my family. This might sound like a some-of-my- best-friends-are homily, but I want to convey that while any racism is an attack on all of us – I’d have done the same with Islamophobic graffiti – it felt personal in a confusing and painful way.

It felt like an attack on my therapist, who lives just yards from the bus stop; an attack on my friends, none of whom I’ve told about this; on long-dead heroes such as Hersch Lauterpacht, the originator of the term “crimes against humanity” and one of the Nuremberg trial prosecutors, who lived round the corner when he first came to Britain. What would he have thought had he seen this vileness just down the street after fleeing the same hatred in Nazi Germany?

Two weeks later, I checked the stop again. Someone had scraped a giant SS and a swastika into the black paint. This was one determined antisemite. At least I hoped it was just one.

I called the council again, and this time spoke to someone very helpful – even though, as I probably should have guessed, she thought the bus company should take responsibility for the stop. She gave me a reference number, and promised that something would be done within 24 hours. The graffiti, and my black square, were both cleaned off soon after that.

I’m left kicking myself that I didn’t act sooner, and have half decided to carry spray paint with me at all times. I wish I’d done something better – I don’t know what it would be, but I feel as much guilt as anger. I’m horrified that, rather than it just being a drunken, impetuous one-off, the person who hates Jews came back and restated their vile bigotry. And what if they come back again? What if there are more of them?

And there are more of them. Last year there was a record number of antisemitic attacks in the UK, according to the BBC. A Jewish charity, the Community Security Trust, said that 767 incidents were reported in the first six months of 2017 – 30% more than in the same period of 2016. There were 80 violent assaults reported, as well as vandalism, hate mail, verbal abuse and graffiti.

I wonder about all the other people who saw that slogan every day for nearly a month, rather than just twice a week: all the people who live nearby, get on and off the buses, walk home past a sign yelling “Jews Out!!!” – albeit in misspelled German. I wonder about the people who watched me take photographs of the graffiti, then spray-paint it out, without comment or reaction. I wonder what I’d have done in Berlin in 1936. What would you do?

• Kay Holmes is a writer and journalist