- Traditional brewer's mark for barrels of "extra strong" beer - extended to other alcoholic beverages and other products having an "extra strong" dimension (varying from washing soap to pornography).
- An indicator of hazard or poison.
- Extra strong - very high quality
- Designating of hardcore pornography.
2012 April 19, Josh Halliday, “Free speech haven or lawless cesspool – can the internet be civilised?”, in the Guardian:
- Other global taboos, such as sex and suicide, manifest themselves widely online, with websites offering suicide guides and Hot XXX Action seconds away at the click of a button. The UK government will come under pressure to block access to pornographic websites this year when a committee of MPs publishes its report on protecting children online.