If security sweeps are the giveaway, former Massachusetts Gov. Mitt Romney may be on the brink of being selected as Sen. John McCain’s (R-Ariz.) vice presidential running mate.

According to sources with strong Michigan ties, the Secret Service has conducted a security sweep of the home of Romney’s sister. Romney was raised in Michigan, where his father served as governor.

However, one campaign operative familiar with the working of a presidential-level campaign cautioned that a sweep of such a location could have been conducted in advance of Romney appearing as a surrogate — not the vice presidential nominee — at an upcoming McCain campaign stop in Michigan.

Any McCain campaign appearance in Michigan would likely include Romney, who remains popular there.

Other sources and some news reports have also suggested that Romney in the last few days might be traveling with a security detail, although exactly who employs this security detail could not be confirmed.

Romney finished first in Michigan’s January GOP presidential primary. McCain finished second in that race.