While some hotels avoid having a 13th floor, others are choosing to skip the number 420, in order to deter cannabis smokers.
To most people it means nothing, but the number 420 has a long association with cannabis and is often used as a code for those in the know.
The Telegraph reported that some hotels have renamed their rooms in a bid to avoid being associated with marijuana smokers - some of whom like to steal room signs and smoke in their rooms as a celebration of the number.
An image posted on Imgur shows a room labelled "419 + 1", with a no smoking symbol in the corner.
In Colorado, where it is legal to smoke cannabis, a hotel chose to stencil the number 420 on a door, rather than deal with the hassle of replacing an often-stolen placard.
Another hotel decided to just avoid the number altogether, skipping from 419 to 421.
While the practice of avoiding the number 420 appears to be a recent trend, hotels have often chosen to skip the number 13 when labelling floors or rooms.
In Chinese superstitions, the number four is considered very unlucky, due to its similarity in pronunciation to the word for death.
As a result, fourth floors are often omitted in hotels and high rise buildings in some East Asian cultures.