That sign usually means no entry for bikes so I was confused for a moment

Don’t signs usually have a line through it when it means “no”, or is that just american signage?

European bike lanes (like this one should probably depict) are round and solid blue with a bike depicted on them.

bike lane

In Europe, lanes, where biking is prohibited are denoted by a round white sign with a relative wide red border (circle) and a bike depicted at its center.

biking prohibited

Is there a problem having a little line through the thing you’re not supposed to do?

/American (sorry) question

That is used for cancelling a previous sign.