Hey @Nerijusz,
Great question!
Exactly as you assumed, those negative values for the $Source property would be representative of the app/integration/API that the profile/contact originated from. You can actually find a glossary of what those negative values represent from our Source Value Reference Help Center article.
To simplify things, I’ve included the chart below for those values and which source they correlate to:
| $source Value | Profile Source |
| -1 | Unknown |
| -2 | Modal |
| -3 | Flyout |
| -4 | Embedded Form |
| -5 | Subscribe Page |
| -6 | Manually Initiated |
| -7 | Twitter |
| -8 | Integration |
| -9 | API |
| -10 | Copied from Another List |
| -11 | Swapped Subscription |
| -12 | Unknown |
| -13 | Manually Initiated |
| -14 | Unsubscribe Page |
| -15 | Unknown Integration |
| -16 | Swapped Subscription |
| -17 | API |
| -18 | Copied from Another List |
| -19 | Spam Complaint |
| -20 | Hard Bounce |
| -21 | 3dcart |
| -22 | BigCommerce |
| -23 | Postmark |
| -24 | Celery |
| -25 | Constant Contact |
| -26 | Zoho |
| -27 | API |
| -28 | ActBlue |
| -29 | Help Scout |
| -30 | Zendesk |
| -31 | Olark |
| -32 | ShopDirect |
| -33 | Mailgun |
| -34 | MadMimi |
| -35 | Lightspeed |
| -36 | Unbounce |
| -37 | Janrain |
| -38 | WooCommerce |
| -39 | Magento |
| -40 | Mandrill |
| -41 | Wufoo |
| -42 | Sendgrid |
| -43 | Mailchimp |
| -44 | Commercev3 |
| -45 | Amazon Web Services |
| -46 | AfterShip |
| -47 | Klaviyo |
| -48 | Salesforce |
| -49 | NeonCRM |
| -50 | Shopify |
| -51 | Volusion |
| -52 | UserVoice |
| -53 | Eventbrite |
| -54 | Kickoff Labs |
| -55 | Amazon Marketplace |
| -56 | Magento 2 |
| -57 | Qgiv |
| -58 | StickyStreet |
| -59 | Segment |
| -60 | Chargebee |
| -61 | Recurly |
| -62 | Stripe |
| -63 | Campaign Monitor |
| -64 | Magento |
| -65 | Classy |
| -66 | Spree |
| -67 | Desk.com |
| -68 | Facebook Audiences |
| -69 | DonorPerfect |
| -70 | Donate.ly |
| -71 | ExactTarget |
| -72 | OpenCart |
| -73 | Funraise |
| -74 | 3dcart |
| -75 | BigCommerce |
| -76 | Postmark |
| -77 | Celery |
| -78 | Constant Contact |
| -79 | Zoho |
| -80 | API |
| -81 | ActBlue |
| -82 | Help Scout |
| -83 | Zendesk |
| -84 | Olark |
| -85 | ShopDirect |
| -86 | Mailgun |
| -87 | MadMimi |
| -88 | Lightspeed |
| -89 | Unbounce |
| -90 | Janrain |
| -91 | WooCommerce |
| -92 | Magento |
| -93 | Mandrill |
| -94 | Wufoo |
| -95 | Sendgrid |
| -96 | Mailchimp |
| -97 | Commercev3 |
| -98 | Amazon Web Services |
| -99 | AfterShip |
| -100 | Klaviyo |
| -101 | Salesforce |
| -102 | NeonCRM |
| -103 | Shopify |
| -104 | Volusion |
| -105 | UserVoice |
| -106 | Eventbrite |
| -107 | Kickoff Labs |
| -108 | Amazon Marketplace |
| -109 | Magento 2 |
| -110 | Qgiv |
| -111 | StickyStreet |
| -112 | Segment |
| -113 | Chargebee |
| -114 | Recurly |
| -115 | Stripe |
| -116 | Campaign Monitor |
| -117 | Magento |
| -118 | Classy |
| -119 | Spree |
| -120 | Desk.com |
| -121 | Facebook Audiences |
| -122 | DonorPerfect |
| -123 | Donate.ly |
| -124 | ExactTarget |
| -125 | OpenCart |
| -126 | Funraise |
| -127 | Facebook Lead Ad |
| -128 | Typeform |
| -129 | Suppressed by Flow |
| -130 | Back in Stock |
| -131 | Back in Stock |
| -132 | mi9 |
| -133 | mi9 |
| -134 | Invalid Email |
| -135 | Merged Profiles |
| -136 | Transferred Memberships |
| -137 | Transferred Memberships |
| -138 | NetSuite |
I hope this helps!
David