proper syntax for itertuples?

[scidam]

You don't need to use loops for this task at all.

Something like this:

df.loc[df.loc[:, 'Close'] > df.loc[:, 'prev'], 'trade2'] = '+'
df.loc[df.loc[:, 'Close'] < df.loc[:, 'prev'], 'trade2'] = '-'
df.loc[df.loc[:, 'Close'] == df.loc[:, 'prev'], 'trade2'] = df.loc[((df.loc[:, 'trade2'] =='+')|df.loc[:, 'trade2'] == '-').last_valid_index()]['trade2']

should work.