Please help me,
I´m looking for some idiom that would fit in the context:
In Slovakia, ticket inspectors don´t wear uniforms because it would be like hunting rabbits with a tambour. = it would be obvious that they are ticket inspectors and people would see them and would get off the bus before the inspectors could check them.

thank you

Hunting rabbits with a tambourine is even less likely to succeed, but you may convert a few to the Salvation Army.

Like undercover police, air marshalls, bailiffs, and the like.  No one knows who they are because they are so obvious.

well, that didn´t help me, I need some idiom to express that if they were uniformed, people would knew who they were and would get off the bus or punch tickets. So something like that. Maybe there´s nothing, but I´m sure that your wonderfully rich language does have something which would express the idea of that.

Sorry,  we are not always serious here, but do have lots of fun.  I know what you are asking, but nothing comes to mind at the moment.  Maybe some other poster
will get involved here, and I’ll give it some thought.

“As plain as the nose on your face” is one way of describing the blindingly obvious, Ovecka.  Hope that helps to sort the wheat from the chaff for you.

Oooo, thank you very much, I like that. I think it helps me a loooooooot.

Just don´t know why didn´t I find this out.