I'd think it's a balance issue and as mainly Axis player I am fine with sign posts being visible.
I've always thought it was just visible to your own side though, since that seemed more logical...
I mean the minefield is bigger than individually placed mines clusters, and if you position them in the right place and right angles they can be hard to detect in themselves.
Why not just remove the signs and give it suppression?
Solves wiping problem (unless you are REALLY not paying attention), retains power, gets rid of the literal signpost telling the enemy where you have mined.
IMO that would only work if suppression also works on retreating units, which it currently does not. It removes an element of the gameplay where you can exploit the feature by just having your men retreat through a minefield and detonate them (being suppressed or not); this does not require deploying engineers with minesweepers.
True, any good opponent with a keen eye will spot any potential place for mines and a signpost is a giveaway, but I think as Ostheer or OKW's Fortification Doctrine, minefields are best used alongside things like bunkers, anyways.
Still, removing signposts from enemy vision and making it cloaked like the mines is something to consider. I don't know if it's possible or easy to make the signposts more detectable so the enemy would at least have to be a bit close to the minefield to give it away.