"I'd like to get a card but I am afraid that someone, like my boss or the police, would know that I use marijuana. Is this completely private?"
Yes, your records are private and cannot be accessed by anyone without a signed release of information. HelloMD does not share patient information and your consults with your physician are private.
Some employers and specific occupations require drug testing. In that case, you will want to disclose truthful information. You should know your employer's policies. You will have to decide, based on your employment situation, if using cannabis is right for you.
Even with the voluntary state ID card, your privacy is protected at the state level, where only a patient number is kept on file. You register for them through your county health department, and some of those (San Francisco and Santa Cruz) destroy your records on the spot. Others keep them on file, but are prohibited from sharing that information by state and federal law. More at: http://www.canorml.org/prop/sb420IDcards.htm.
Your health information is protected in the same manner as any medical provider would protect it. All records are kept in a manner compliant with state and federal law. No information is shared without your permission.