Usually you will see something like 7018-H4R. The manufacturers must think the cost of including the letter "E" in the classification to be extraneous and expensive to print.

The H4 indicates the electrode is capable of producing no more than 4 ml of diffusible hydrogen per 100 g of weld deposit assuming it was properly stored in an electrode holding oven that is turned on and set to the proper temperature (I mention that because I had a client store the electrodes in the oven, but though turning it on was a waste of electricity). The "R" indicates the flux covering has been formulated to resist moisture pick-up for a period of time in excess of the "normal" E7018 electrode. How long the electrode can be exposed to ambient conditions and still meet the low hydrogen requirements is stipulated by the appropriate welding standard or established by tests.

Best regards - Al