Paper flyers in your mailbox, and billboards in people's gardens, are some age-old and very common forms of advertisement during elections I've seen in multiple countries in Europe
It's pretty nice in that I can throw it all straight into the recycling bin!
The most common form of political advertising by volume is probably unauthorized propaganda posters on public infrastructure, yeah. Those are annoying. Also stickers on traffic light poles and similar places.
I mostly see them on tv, public billboards and light poles.