This Ash Wednesday, thousands of Mexicans demanding justice for the 43 students from a teachers college in Iguala who disappeared last September, took their protests to the world of social media.

The disappearance and alleged mass murder of the 43 students in the state of Guerrero has torn apart the country and led to constant protests both in and out of Mexico.

The students were on their way to a protest over school hiring practices when they were stopped by police who shot at their buses and then allegedly handed them over to a criminal gang.

According to Mexico's attorney general Jesus Murillo Karam, the missing were then killed by the gang and their bodies were burnt at a rubbish dump.

So far only one body has been identified, and the explanation offered by the attorney general has been rejected by families of these students as well activists.

The popular suspicion is that the Mexican military played a role in these events.

Keep the focus on the missing 43, the Twitter account a #43NoSonCeniza ("43 Are Not Ashes") has been getting a lot of traction in Mexican social media.

In a move that plays off the pathos of Ash Wednesday, a Christian holiday that marks the start of lent, activists are asking people to spread word of the protest by painting their foreheads with the number 43, and uploading the pictures online.

Images of the ash marked protesters can be seen at #Ayotzinapa.

The highly symbolic campaign was created by a Mexico city-based artists' collective called ¿qué hacer? (What to do?).

Explaining to the BBC how they wanted to appropriate a Catholic ritual into an expression of political protest, an anonymous member of the group stated that, "We want people to remember, and keep remembering that the disappearance of the 43 students is still unresolved. To show our discomfort with the official version of facts, which tries to state that the students were incinerated and the military had nothing to do with it. Too many lies."

The idea seems to be working. As reported by the BBC, the hashtag has already been mentioned more than 6,000 times.