San Francisco 49ers quarterback Colin Kaepernick -- who has come under fire for his silent protest at a recent game of the U.S. national anthem -- has been wearing a subtle jab at police to team practice sessions. writer Philip Lewis posted photos to Twitter of a pair of socks Kaepernick wore to 49ers practice that portrayed police as pigs, a longtime derogatory term for law enforcement officers.

Lewis noted that the photos were taken on Aug. 10, well before controversy erupted over Kaepernick's national anthem protest. The quarterback refused to stand during the playing of the national anthem at a televised game last week.

Kaepernick has long made a habit of sitting during the anthem, but commentators only made an issue out of it recently.

Conservative critics have rushed to attack Kaepernick's patriotism, while others -- like NBA legend and U.S. cultural ambassador Kareem Abdul-Jabbar -- have insisted that our nation's freedoms support political protest and open discourse.

In the past, Kaepernick has made known his distaste for both 2016 presidential nominees. He has called Donald Trump a racist, but also said that Democratic nominee Hillary Clinton should "be in prison" for her handling of classified information while Secretary of State.