The four-character chop, yuxin wukui, may be translated as: 'With a Clear Conscience'.
The two characters, Shangjun, carved within a cartouche on the top facing side is the artist's name for the carver Zhou Bin from Fujian province who was active during the mid-17th century. The extremely fine carving in rendering archaistic birds and dragons, and the signature within a small cartouche are characteristics of Zhou Bin's work. For soapstone examples of Zhou Bin's work, see Arts from the Scholar's Studio, The Oriental Ceramic Society of Hong Kong, nos. 43 and 44: a pair of seals and a seated Luohan respectively.