Is it true that Eagle-Lion Films, in the 1940s, had on its logo "Sic Pro Optima", roughly meaning "Thus for greatness"?

I believe it to be true.

Eagle-Lion Films had its genesis in England, as a small studio founded in 1946 by Arthur Krim that soon came under the ownership of film mogul J. Arthur Rank. It broadened its enterprise to the States by acquiring the PRC studios in 1948, and quickly became one of the most respected producers on Hollywood's "Poverty Row". They also distributed other studios' output both here and abroad, such as those produced by David O. Selznick and by Rank himself.

Krim left Eagle-Lion in 1949 (he would later be offered the leadership of United Artists), and the company continued to release and distribute a much-diminished output. By 1954 the company was no more, and the old studio on Santa Monica Blvd.

The organization's logo was a plaster-looking circular plaque has bas-relief images of a soaring eagle on top and a lion striking a pose on a ribbon (bearing the legend "SIC PRO OPTIMA") beneath, with the words "Eagle-Lion Films" in Edwardian Script superimposed across the center, between the two beasts.

https://closinglogosgroup.miraheze.org/wiki/Eagle-Lion_Distributors,_Inc.