PCA seems to be very popular in dimension reduction applications and for extracting the top PCs which explain the data. One such application in futures is on the term structure to obtain the level, slope and curvature components.
However, since the sign of the PCs can be anything(because +EigenVector and -EigenVector are both valid solutions), how do we infer anything about the slope of the term structure by using the slope PC? The slope could be either positive or negative since the sign of PC is not significant.
How do I handle this sign issue when working with PCA?