The return value from that function is a data frame, so the question is how to make a column of a data frame print with a percentage sign.
Reproducible example follows.
> require(PerformanceAnalytics)
> data(managers)
> tb = table.AnnualizedReturns(managers[,1],Rf=0)
> tb
HAM1
Annualized Return 0.1375
Annualized Std Dev 0.0888
Annualized Sharpe (Rf=0%) 1.5491
Now we define a new class and a format function that displays with a percent sign:
> format.pc = function(x,...){sprintf('%0.2f%%',x)}
> class(tb[,1])="pc"
And now, as if by magic:
> tb
HAM1
Annualized Return 0.14%
Annualized Std Dev 0.09%
Annualized Sharpe (Rf=0%) 1.55%
The underlying values have not been changed:
> tb[,1]
[1] 0.1375 0.0888 1.5491
attr(,"class")
[1] "pc"
they are just in a vector of this new class.