From my experience, I was able to carry a Bic lighter with me in my check in baggage.
"Dot" is "DOT" - Department of Transportation. So DOT Approved means "Approved by the Department of Transportation".
What does DOT and SAE approved means
No.
It means something has been approved by the Department of Transportation.
In most states DOT helmets are required.
By dot helmet do you mean a Department of Transportation approved type ?
Department Of Transportation has approved
means that dot has not approved this tank to drive
Is illegal
All helmets must be DOT approved and have the DOT sticker on them, in the US, when helmets are required.
You dot the letter 'i' because the letter 'i' was originally written that way in lower case, so we must always dot the lower case letter 'i'.