What was meant was
Abra (formal imperative for abrir, to open)
Confusion about which words take a silent H and which don't is extremely common among Mexicans, Mexican Americans and Chicanos. If someone has a little trouble with this aspect of spelling, by no means can we assume the person is ignorant, stupid or uneducated.
There is a certain charm in this sign. It is written in a natural way, and reads like it was designed by someone bilingual. A scenario that suggests itself is that the person who wrote it works at the bus company, was raised speaking Spanish at home and some other settings, but had formal schooling primarily or entirely in English.
A native speaker of Spanish will imagine the sound of the word and parse it accordingly. Learners of Spanish understandably lean more on the written letters to figure things out, and might find it confusing.
Regarding the capitalization: In English it's normal to use title case for signs; it's only natural that a bilingual sign carry that over to the Spanish. See https://ux.stackexchange.com/a/28299/69183 (regarding headings and instructions in websites: "Title case propagates in Spanish pages because it's easier to write and because of the influence of the USA sites").