Basically anything that is designed only for use within the company that engineered it, and will not be made available to the public. It's generally referred to as an "industrial exemption".
I believe the trend in recent years has been for state licensing boards to try and do away with industrial exemptions as much as practical, but I think they're still around and in use to some degree as far as I know. Just like licensure in general, it varies from state to state.
It's all I'm saying. If you're not a PE, don't make yourself available to the public as an engineer who can perform professional services.