Rashi ji, The names and emblems (prevention of improper use) Act, 1950 in its Section 3 reads as :
3. Prohibition of improper use of certain emblems and names
Notwithstanding anything contained in any law for the time being in force, no person shall, except in such cases and under such conditions as may be prescribed by the Central Government use, or continue to use, for the purpose of any trade, business, calling or profession, or in the title of any patent, or in any trade mark or design, any name or emblem specified in the Schedule or, any colourable imitation thereof without the previous permission of the Central Government or of such officer of Government as may be authorised in this behalf by the Central Government.
So, a business man cannot use the national flag on his visiting card without Govt permission.