Travis (DeNiro) changed his hairstyle to Mohawk near the end of Taxi Driver. I guess he changed his hairstyle to avoid the secret service agent (the one he ridiculed before), or was there some other reason to? And why did he choose Mohawk? Was there any specific reason behind it?
During World War II, many American GIs, notably paratroopers from the 101st Airborne Division wore mohawks to intimidate their enemies. It was also occasionally worn by American troops during the Vietnam War & Travis was Vietnam war veteran.
So he was preparing for his war with all his exercises, drill, hairstyle, etc.