Short Answer the code below will put "<--Empty" in the cell next to the empty cell:
Range("E:E").Find(vbNullString, [E3], , , , xlNext).Offset(0,1) = "<--Empty"
The Rnage.Find method returns cells matching the criteria sequentially. To return an adjacent cell, use the Range.Offset method. Rather than selecting, just type the string into the cell.
Long Answer: Personally, I try not to use the Range.Find method because all of those arguments you did not specify default to whatever your PC had last. This can cause different behavior on different PCs. Instead, I would use a for loop to loop through the range of interest
For i = 1 to Max
if RangeOfInterest(i,1) = vbNullString then RangeOfInterest(i,1).Offset(0,1) = "<--Empty"
Next i