I walked past this sign the other day near Dingxi MRT station and was reminded of how often Taiwanese people use simpler variants of some characters when writing some of the more complex Chinese characters, many of which were adopted in China as the standard simplified version of the character:
[Incurs a] fine [of]
It’s not OK to throw bags inside
Here 「亂」, meaning here “carelessly” or “against the rules”, is written using the variant 「乱」, which is identical to its simplified form.
This variant form is listed in the MOE’s Variant dictionary: