Since you live in Homer, then you have the Syracuse Main through your town. I believe you may be asking how, by sight, can you identify the specific trains. Having a scanner is a big assist to this, but the following may give you some insight. On the Northjern division, in your area, there is an SY-1 crew, based out of Syracuse(hence the SY designation) that works 5 days a week. On their rest days, there will usually, but not always be an SY-X(X = Extra Crew). This symbol may also be used for crews that do other than customer work, such as running the through traffic to/from CSX. these trains can usually be identified by the numbers of garbage cars. They are usually loaded going to Syracuse and empty going south to Binghamton(and eventually NJ)
For a while last year, they had a crew based out of Cortland, and referred to them as the CL-1. The local crew that travels the main in your area will usually have the same locomotive on several days. Also, they will have several tank cars for Suit Kote in Cortland, as well as lumber cars for Gutchess and Bestway in the Cortland area and the Roundhouse Mill as well.
There is significant and solid customer work on this line, and if you are able to get to Cortland, or trackside at all, then you should be able to witness the SY-1 and their work. But if you are referring to train identity by commodities carried, the SY-1 in your back yard is a good place to start. There will be days when the traffic from Binghamton to Syracuse will come north with a BH(Binghamton crew and symbol), and this will most oftern be the SU-99 traffic from NJ that is destined to CSX. Again, as i noted above, the loaded debris cars are a tip off. I hope this helkps answer your question somewhat. if not, let us know in the forum.
I know I'm getting old... My insurance company sent me only half a calendar this year!