The number eighteen with a red stroke through it, indicating a location where a person must be aged 18 or above to enter. Often used online to indicate adult or NSFW content.
Google's design includes the text "under" above the number eighteen.
The Samsung version of this emoji previously displayed the number 19. This may have been due to the practice of counting the first year of life as one instead of zero in parts of East Asia such as South Korea (the location of the Samsung Headquarters).
No One Under Eighteen was approved as part of Unicode 6.0 in 2010 under the name “No One Under Eighteen Symbol” and added to Emoji 1.0 in 2015.
U+1F51E
? No one under eighteen symbol