This is an interesting sentence, though I think this expression is quite verbal. Reading "一边望着站牌对照", you will find two verbs in the sentence, "望着" and "对照". The meaning of this sentence is "facing the sign and compare it with the map". "一边望着站牌" is already a complete sentence in grammar, but its meaning is not completed. People are confused why do they face the sign? Therefore, we added "对照" at the end to indicate that they faced the sign for comparing the sign with the map. You cannot connect two verbs directly, like "望着对照". It doesn't make sense. Actually, to supplement something at the end of a sentence ungrammarly to complete the meaning is not unusual in Chinese, so sometimes you need to comprehend it in an abstract way.

Let's try put it in this way : That is like "it badly hurt me" = "it hurt me , badly" 一边望着"对照站牌"= 一边望着站牌,and do a 對照 verb can be a adj. in moden Chinese , and adj. can be a verb too. Or think like this : The "对照站牌" become a thing, which you can say it separately in sentence : There is a 站牌 , to be used for doing "對照" Or not separate them : There is a 對照站牌 Maybe this is about a moden Chinese speaking logic? We can't change "對照" into "公交" for another example, just because "公交" can not be a verb. So , we can say "公交站牌" , but we can't say a 站牌 to be used for doing "公交"，we can't say 一边望着站牌公交