The Eclipse Foundation requires that all contributions be signed off by contributors who have signed the Eclipse Contributor Agreement (that is, they need to include a "Signed-off-by" field in the footer). This is different from signing commits. I'm actually curious to see how requiring that commits be signed actually works in practice. I'm concerned, though, that requiring it would be yet another barrier and we should be all about lowering barriers at this point.
Regarding commit size... Per the IP Policy, any commit of more than 1KLOC needs to be reviewed by the IP Team. I know that there are some committers who encourage contributors to chop up their contributions to keep the commit size down to avoid this requirement. Please don't do this.
Having said all that, IMHO, it is completely unreasonable to expect a committer to review a very large contribution. Further, it is better for everybody, committers and contributors, to push work in incremental chunks (reviewing is easier, and it's easier for others to keep up with the changes). Massive code dumps just make it hard for others to collaborate.
Wayne