46 CFR §98.30-33

1. (a)If the vessel is moored, no person may transfer to or from a portable tank or IBC a product with a flashpoint of less than 300 °F unless the person in charge displays a—
   1. (1)Red flag by day; and
   2. (2)Red electric lantern by night.
2. (b)If the vessel is at anchor, no person may transfer to or from a portable tank or IBC a product with a flashpoint of less than 300 °F unless the person in charge displays a red flag.
3. (c)The signal required in paragraphs (a) and (b) of this section must be visible on all sides of the vessel.