For most shops, if not all, it won't show up as anything related to marijuana on your statement. It's similar to if you purchase porn or deposit money into an online poker (in the US anyway since online poker is illegal).
I can't say what herbies head shop will come up as, so maybe someone else can tell you for sure. I looked on their site and it says the FAQ section is under construction?? I've only ordered from Nirvana and it definitely didn't say anything related to marijuana.
If you're still worried about it, you could always get a gift card or pre-paid card from Visa or Mastercard and pay with that.