General Sir James Willoughby Gordon, Quarter-Master General to the Forces 1811 - 1851 - MP for Launceston 1829 - 1831
Vice-Admiral William Gordon - MP for Aberdeenshire 1820 -1854
On close inspection the 'J' which precedes the 'W' on Sir James Willoughby Gordon's signature (top) makes a third vertical line preceding the 'Gordon' part of the signature whereas in the case of William Gordon (bottom) there are only two such vertical lines. Other giveaways include the heavy underlining of Sir James Willoughby Gordon's signature as well as elsewhere on the envelope front (top). Another giveaway is if William Gordon's front is sent from Aberdeen, although this example is sent from London a great many examples that I've seen are addressed from Aberdeen. Usually the dates of course are another key clue in correctly identifying the signature, however in this case the two men were in office at the same time as one another for a very long time, from 1820 to 1851 in fact. Clearly though an example prior to 1820 is likely to be that of Sir James Willoughby Gordon and similarly one dated after 1851 couldn't be his.