One or two well placed minefields is affordable and can make a big difference vs USA spam. Its best to place them defensivley where its hard work for detectors to clear them (appart from retreat paths which is a cheeky one, need good timming though).
Even if he did see the sign, they still help win engagements by defending an MGs flank etc. Once you know hes seen it, just send somthing to see off any engies that come.
Honestly, I rarely see axis players use mines in a lot of my 2v2 games. Mines become even less used the higher up you get...
But when they do use mines, it's like a mind fuck because of how good they are and how I wasn't expecting it at all.
People always refer to OST as fuel starved, or munition starved factions. I don't see how, you upgrade LMG's on your grens, which Soviets can't do w/ Cons, but they're busy spending 20 munitions to Hoorah, and 15 to molotov, everytime... do that twice and you already covered the cost of a single LMG for a Gren.
Putting MG's on all your tanks isn't exactly something you need to do right away, you can always lay mines instead. Maybe I'm too old school, it's been like 2000hrs and years but I can remember needing to use mines to win engagements properly. To stop blitzing tanks from just rushing in and rushing out, or being flanked. Mines just became another natural tool in my arsenal, and I use them with as much effect as OST/OKW as I do w/ the Soviets.