I think this question also depends on where you live. Some states punish law abiding citizens for merely owning a firearm, let alone carrying or actually using it for self-defense. In Arizona, if you have a reasonable suspicion that your safety is in danger by the actions of a third party you can initiate a "defensive display" as its called in Arizona State Law. You can inform of the presence of a firearm, expose or display the firearm, or place one's hand on the firearm as to indicate the capability to defend oneself:
A.R.S. §13-421. Justification; defensive display of a firearm; definition
(SB 1243, enacted July 13, 2009, effective Sep. 30, 2009.)
A. The defensive display of a firearm by a person against another is justified when and to the extent a reasonable person would believe that physical force is immediately necessary to protect himself against the use or attempted use of unlawful physical force or deadly physical force.
B. This section does not apply to a person who:
1. Intentionally provokes another person to use or attempt to use unlawful physical force.
2. Uses a firearm during the commission of a serious offense as defined in section 13-706 or violent crime as defined in section 13-901.03.
C. This section does not require the defensive display of a firearm before the use of physical force or the threat of physical force by a person who is otherwise justified in the use or threatened use of physical force.
D. For the purposes of this section, "defensive display of a firearm" includes:
1. Verbally informing another person that the person possesses or has available a firearm.
2. Exposing or displaying a firearm in a manner that a reasonable person would understand was meant to protect the person against another's use or attempted use of unlawful physical force or deadly physical force.
3. Placing the person's hand on a firearm while the firearm is contained in a pocket, purse or other means of containment or transport.
The state of Washington doesn't have such a defensive display law in place but, it does have a solid brandishing law.
RCW 9.41.270
Weapons apparently capable of producing bodily harm — Unlawful carrying or handling — Penalty — Exceptions.
(1) It shall be unlawful for any person to carry, exhibit, display, or draw any firearm, dagger, sword, knife or other cutting or stabbing instrument, club, or any other weapon apparently capable of producing bodily harm, in a manner, under circumstances, and at a time and place that either manifests an intent to intimidate another or that warrants alarm for the safety of other persons.
(2) Any person violating the provisions of subsection (1) above shall be guilty of a gross misdemeanor. If any person is convicted of a violation of subsection (1) of this section, the person shall lose his or her concealed pistol license, if any. The court shall send notice of the revocation to the department of licensing, and the city, town, or county which issued the license.
(3) Subsection (1) of this section shall not apply to or affect the following:
(a) Any act committed by a person while in his or her place of abode or fixed place of business;
(b) Any person who by virtue of his or her office or public employment is vested by law with a duty to preserve public safety, maintain public order, or to make arrests for offenses, while in the performance of such duty;
(c) Any person acting for the purpose of protecting himself or herself against the use of presently threatened unlawful force by another, or for the purpose of protecting another against the use of such unlawful force by a third person;
(d) Any person making or assisting in making a lawful arrest for the commission of a felony; or
(e) Any person engaged in military activities sponsored by the federal or state governments
Though if in a state like NY, NJ, or Maryland -- good luck.