San Francisco 49ers quarterback Colin Kaepernick has been wearing an interesting pair of socks during practice.

Kaepernick ignited a nationwide debate last Friday when he chose to sit during the national anthem at a home pre-season game in San Francisco. CBS Sports and a handful of Twitter users noticed that Kaepernick has been wearing practice socks that depict little cartoon police officers as pigs:

New photo reveals #Kaepernick wearing socks depicting police officers as “pigs”. CC: @robbware pic.twitter.com/WWNP2gqpVL — Spark Sports (@Spark_Sports_) September 1, 2016

Following his public protest of the anthem, Kaepernick disparaged law enforcement, and said that, “people [police officers] are on paid leave while people of color are killed.” Kaepernick explained his perspective on race relations in America and said that, “I’m going to continue to stand with the people that are being oppressed.”

The San Francisco Police Officers Association sent a letter to the NFL and San Francisco 49ers Monday, denouncing Kaepernick for his “ill-advised statements,” and “total lack of sensitivity towards police officers.”

Police unions in San Francisco and elsewhere have invited Kaepernick to visit one of their training academies to experience the work of law enforcement officials. You can read the full letter from the union denouncing Kaepernick here.

Kaepernick will face the San Diego Chargers Thursday. The Charges will be hosting their annual “Salute to the Military” night at Qualcomm Stadium.

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