The 
signs are only in EE, added most probably by Chopin in the base text to this edition. The sign in bar 18, having a form of an accent under the chord on the 2nd beat of the bar, is almost certainly a result of misunderstanding of the entry of Chopin – in the original graphical layout the chords in the L.H. are divided between both staves, as a result of which the written between the staves can be understood as referring to the L.H. only (similarly in bar 26). In the main text we suggest a much more likely interpretation of these signs, given in EE in the recapitulation (bars 72 and 80).
Compare the passage in the sources »
category imprint: Interpretations within context; Differences between sources
issues: EE inaccuracies, Authentic corrections of EE
notation: Articulation, Accents, Hairpins