He spent a summer and half driving legendary scout Charley Barrett who was working for Branch Rickey, the general manager of the St. Louis Cardinals.

He was Wagoner's first manager having heard him on a local broadcast from a butcher shop in West Plains, Missouri; produced his first hit, "A Satisfied Mind", in Springfield; and signed him to an RCA Records contract in 1951.

From 1954-1961, Siman and Mahaffey were managing vice presidents of Foster's Crossroads TV Productions, and co-executive producers of ABC-TV's Ozark Jubilee, the first popular country music series on network television.

In April, 1954, Siman lured Red Foley to Springfield to host the program over a bottle of Jack Daniel's whiskey at the Andrew Jackson Hotel in Nashville, Tennessee.

Especially noteworthy are the standards "The Letter" (Two-time Grammy Nominee) (#1 1967) - the song would be covered by artists all around the world but would have the distinction of being a top 20 single in the US three times in a span of four years (’67, ’69 and ’70) with the Boxtops, the Arbors and Joe Cocker, and Always on My Mind.

The firm obtained copyrights for national country hits including Little Jimmy Dickens' smash "A-Sleeping at the Foot of the Bed" (1950), "Trademark" with Carl Smith (1953) and Johnny Mullins' novelty tune "Company's Comin'" (1954).

Other #1 singles in the 1970s included "I See the Want to in Your Eyes" with Conway Twitty and Rocky (song) by Dickie Lee (also a top 10 pop hit with Austin Roberts.

His son, Scott Siman, is an entertainment executive in Nashville who manages and oversees the multi-faceted career of superstar Tim McGraw, as well as managing numerous other country music artists and publishing multiple #1 country songs such as "Make You Miss Me" by Sam Hunt, "Break Up With Him" by Old Dominion, "Save it For a Rainy Day" by Kenny Chesney and "It's 5 O'clock Somewhere" by Alan Jackson and Jimmy Buffett.