What was the purpose of putting blood on the doorposts? The common (mis)perception is that it was to differentiate between Jewish and egyptian houses, so Hashem would only slay the firstborn in Egyptian houses, but not in Jewish ones.
Did Hashem really need their assistance in order to differentiate the houses? Would Hashem not know which house belonged to a Jew and which to an Egyptian?
That can't be the reason for the blood. On the verse in 12:13 "ולא יהיה בכם נגף" Rashi explains to us that if an Egyptian firstborn was in a Jewish house, that would not protect him and he would still be smitten and a Jew in an Egyptian home would not be harmed..
So what was the purpose of the blood on the soorposts?
Rashi says the blood was to show Hashem that they were busying themselves with the mitzvos and then Hashem would skip over them.
There are times where a person can just quietly do his thing and move along. There are other times where that is not enough. One, sometimes, needs to stand up and be counted. One needs to say out loud which team he is on and who he is loyal to.
This is one of those times. Put the blood on your doorpost. That will show Hashem that you are declaring you are on Gods team.