This system uses one abundance code and one or no status code to express the "Normal Status" of each species.  An example of this it the Behle and Perry checklist from 1975, which is a 6" x 5" folded over piece of heavy paper, with the 390 species for Utah at that time.  (Here's a link to photos of that checklsit)

Here's an example of some of the codes:

Lesser Scaup    CT
Ruddy Duck      CS 
Horned Grebe    RT 
Eared Grebe     CS
Band-t. Pigeon  UP 

This system was use in 1985 and 1990 for state checklists by Mark Bromley and Merrill Webb, but in 1998 was changed to the "present system" in the official Record Committee checklist.

Subcommittee rationale:
"It's simple, yet is usable in the field as a pocket field checklist."  " I agree that a more comprehensive "official" checklist with added information is also needed...but that can be modified, if needed, from our "official" list when it is completed in whatever format we decide."
               

Here's an example of some codes from this system:

Least Sandpiper  U___
Mallard          CUCC
Green Heron      RR_R
Snowy Egret      U_U_
Inca Dove        __R_

The creation of this checklist could probably be facilitate by use of an eBird bar chart for Utah's bird for the last 10 years - here's a link to that "eBird report": species in Utah over that last 10 years:
 
Subcommittee rationale:
"I would rather not oversimplify the checklist since I think it would be doing a disservice to the users of the checklist and only confuse them with generalized codes.
[The Four Season system] gives the most detailed and accurate accounting of the birds in Utah. It is also cleaner looking and more functional than our current checklist since each birds code would be standardized and the user of the checklist could just look at the season they are wondering about and find which species are around then."
            

Here's an example of some codes from our present system:

Lesser Scaup        CT,RS,UW
Ruddy Duck          CP
Horned Grebe        UT,RW
Eared Grebe         CS,RW
Band-tailed Pigeon  US

Subcommittee rationale:
It's the system we've been using since 1998, so would be easy to update.  It describes the occurrence of each species in a simple yet fairly accurate way.

Comments by Mark:
Since there is no committee here in San Blas, nor any existing checklists, I’ve been writing my own for many years now.

I’ve had a chance to see what works “best,” in terms of efficiently imparting the most information possible.

My opinions on the three formats presented are as follows:

1) This system is too simple, a bit arbitrary, and doesn’t offer enough information. It goes to far towards simplicity, in my opinion.

2) I’m not very keen on this one, either. Although it tries to be a simplified bar chart, I think that 3-month quarters isn’t a fine enough resolution, and doesn’t fit the cycle of most birds very well. We could make this better by defining “winter” as Dec-Mar, “spring” as April-May, “summer” as June-July, and “fall” as Aug-Nov., that would fit the annual cycles of most Utah birds better. My other objection is that it’s not an easy layout to read, and would have more letters than necessary for species whose abundance doesn’t vary through the year.

3) This is my favored system, and closest to what I use, though I also include other letters and symbols to give even more information.

But I think one of the most important aspects of any system is how the elements are defined. This is where you can add clarity to a cryptic and arbitrary system.