All lives matter
All lives matter is a slogan originally used by those who disagreed with the Black Lives Matter movement which began in 2013. Although slogans with similar meanings have been used for centuries, the specific phrase "all lives matter" was formulated to appropriate the phrase "black lives matter."
Devoid of context, the statement "all lives matter" is a very positive slogan that I agree with, however, because it was created to oppose the black lives matter movement, whose stated goal is to fight racism, I see "all lives matter" as a dog whistle for racism. It would be wonderful if everyone believed that all lives matter equally, but racism still exists, so clearly they do not.
When determining the motive behind the slogan, it's important to look at who uses the phrase "all lives matter" compared to those who use "black lives matter." In general, "all lives matter" is used by people who see very little impact from racism (e.g., white people, rich people, etc.) while those who use "black lives matter," are impacted much more (e.g., black people, poor people, etc.). To me, this helps put the phrase into context and demonstrates why saying "all lives matter" is similar to saying, "shut up about racism."
The slogan "black lives matter," wasn't just appropriated by white people to "all lives matter," but also to "blue lives matter" and "white lives matter." Those who use these phrases are inadvertently demonstrating that they understand how it is possible to identify a problem, like the dangers of being a police officer, without implying that police officers are more important than everyone else.